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Extracted from https://github.com/denoland/deno/pull/17815
Optimise Buffer's string operations, most significantly when dealing
with ASCII and UTF-16. Base64 and HEX encodings are affected to much
lesser degrees.
## Performance
### String length 15
With very small strings we're at break-even or sometimes even lose a tad
bit of performance from creating a `DataView` that ends up not paying
for itself.
**This PR:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 1.15 µs/iter 871,388.6 (728.78 ns … 1.56 µs) 1.23 µs 1.56 µs 1.56 µs
Buffer.from base64 string 1.63 µs/iter 612,790.9 (1.31 µs … 1.96 µs) 1.77 µs 1.96 µs 1.96 µs
Buffer.from utf16 string 1.41 µs/iter 707,396.3 (915.24 ns … 1.93 µs) 1.61 µs 1.93 µs 1.93 µs
Buffer.from hex string 1.87 µs/iter 535,357.9 (1.56 µs … 2.19 µs) 2 µs 2.19 µs 2.19 µs
Buffer.toString ascii string 154.58 ns/iter 6,469,162.8 (149.69 ns … 198 ns) 154.51 ns 182.89 ns 191.91 ns
Buffer.toString base64 string 161.65 ns/iter 6,186,189.6 (150.91 ns … 181.15 ns) 165.18 ns 171.87 ns 174.94 ns
Buffer.toString utf16 string 292.74 ns/iter 3,415,959.8 (285.43 ns … 312.47 ns) 295.25 ns 310.47 ns 312.47 ns
Buffer.toString hex string 89.61 ns/iter 11,159,315.6 (81.09 ns … 123.77 ns) 91.09 ns 113.62 ns 119.28 ns
```
**Main:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 1.26 µs/iter 794,875.8 (1.07 µs … 1.46 µs) 1.31 µs 1.46 µs 1.46 µs
Buffer.from base64 string 1.65 µs/iter 607,853.3 (1.38 µs … 2.01 µs) 1.69 µs 2.01 µs 2.01 µs
Buffer.from utf16 string 1.34 µs/iter 744,894.6 (1.09 µs … 1.55 µs) 1.45 µs 1.55 µs 1.55 µs
Buffer.from hex string 2.01 µs/iter 496,345.8 (1.54 µs … 2.6 µs) 2.26 µs 2.6 µs 2.6 µs
Buffer.toString ascii string 150.16 ns/iter 6,659,630.5 (144.99 ns … 166.68 ns) 152.4 ns 157.26 ns 159.14 ns
Buffer.toString base64 string 164.73 ns/iter 6,070,692.0 (158.77 ns … 185.63 ns) 168.48 ns 175.74 ns 176.68 ns
Buffer.toString utf16 string 150.61 ns/iter 6,639,864.0 (148.2 ns … 168.29 ns) 150.93 ns 157.21 ns 168.15 ns
Buffer.toString hex string 94.21 ns/iter 10,614,972.9 (86.21 ns … 98.75 ns) 95.43 ns 97.99 ns 98.21 ns
```
### String length 1500
With moderate lengths we already see great upsides for `Buffer.from()`
with ASCII and UTF-16.
**This PR:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 5.79 µs/iter 172,562.6 (4.72 µs … 4.71 ms) 5.04 µs 10.3 µs 11.67 µs
Buffer.from base64 string 5.08 µs/iter 196,678.9 (4.97 µs … 5.76 µs) 5.08 µs 5.76 µs 5.76 µs
Buffer.from utf16 string 9.68 µs/iter 103,316.5 (7.14 µs … 3.44 ms) 10.32 µs 13.42 µs 15.21 µs
Buffer.from hex string 53.7 µs/iter 18,620.2 (49.37 µs … 2.2 ms) 54.74 µs 72.2 µs 81.07 µs
Buffer.toString ascii string 6.63 µs/iter 150,761.3 (5.59 µs … 1.11 ms) 6.08 µs 15.68 µs 24.77 µs
Buffer.toString base64 string 460.57 ns/iter 2,171,224.4 (448.33 ns … 511.73 ns) 465.05 ns 495.54 ns 511.73 ns
Buffer.toString utf16 string 6.52 µs/iter 153,287.0 (6.47 µs … 6.66 µs) 6.53 µs 6.66 µs 6.66 µs
Buffer.toString hex string 3.68 µs/iter 271,965.4 (3.64 µs … 3.82 µs) 3.68 µs 3.82 µs 3.82 µs
```
**Main:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 11.46 µs/iter 87,298.1 (8.53 µs … 834.1 µs) 9.61 µs 83.31 µs 87.3 µs
Buffer.from base64 string 5.4 µs/iter 185,027.8 (5.07 µs … 7.49 µs) 5.44 µs 7.49 µs 7.49 µs
Buffer.from utf16 string 20.3 µs/iter 49,270.8 (13.55 µs … 649.11 µs) 18.8 µs 113.93 µs 125.17 µs
Buffer.from hex string 52.03 µs/iter 19,218.9 (48.74 µs … 2.59 ms) 52.84 µs 67.05 µs 73.56 µs
Buffer.toString ascii string 6.46 µs/iter 154,822.5 (6.32 µs … 6.69 µs) 6.52 µs 6.69 µs 6.69 µs
Buffer.toString base64 string 440.19 ns/iter 2,271,764.6 (427 ns … 490.77 ns) 444.74 ns 484.64 ns 490.77 ns
Buffer.toString utf16 string 6.89 µs/iter 145,106.7 (6.81 µs … 7.24 µs) 6.91 µs 7.24 µs 7.24 µs
Buffer.toString hex string 3.66 µs/iter 273,456.5 (3.6 µs … 4.02 µs) 3.64 µs 4.02 µs 4.02 µs
```
### String length 2^20
With massive lengths we the difference in ASCII and UTF-16 parsing
performance is enormous.
**This PR:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 4.1 ms/iter 243.7 (2.64 ms … 6.74 ms) 4.43 ms 6.26 ms 6.74 ms
Buffer.from base64 string 3.74 ms/iter 267.6 (2.91 ms … 4.92 ms) 3.96 ms 4.31 ms 4.92 ms
Buffer.from utf16 string 7.72 ms/iter 129.5 (5.91 ms … 11.03 ms) 7.97 ms 11.03 ms 11.03 ms
Buffer.from hex string 35.72 ms/iter 28.0 (34.71 ms … 38.42 ms) 35.93 ms 38.42 ms 38.42 ms
Buffer.toString ascii string 78.92 ms/iter 12.7 (42.72 ms … 94.13 ms) 91.64 ms 94.13 ms 94.13 ms
Buffer.toString base64 string 833.62 µs/iter 1,199.6 (638.05 µs … 5.97 ms) 826.86 µs 2.45 ms 2.48 ms
Buffer.toString utf16 string 79.35 ms/iter 12.6 (69.72 ms … 88.9 ms) 86.66 ms 88.9 ms 88.9 ms
Buffer.toString hex string 31.04 ms/iter 32.2 (4.3 ms … 46.9 ms) 37.21 ms 46.9 ms 46.9 ms
```
**Main:**
```
benchmark time (avg) iter/s (min … max) p75 p99 p995
-------------------------------------------------------------------------------------------------------------------- -----------------------------
Buffer.from ascii string 18.66 ms/iter 53.6 (15.61 ms … 23.26 ms) 20.62 ms 23.26 ms 23.26 ms
Buffer.from base64 string 4.7 ms/iter 212.9 (2.94 ms … 9.07 ms) 4.65 ms 9.06 ms 9.07 ms
Buffer.from utf16 string 33.49 ms/iter 29.9 (31.24 ms … 35.67 ms) 34.08 ms 35.67 ms 35.67 ms
Buffer.from hex string 39.38 ms/iter 25.4 (38.66 ms … 42.36 ms) 39.58 ms 42.36 ms 42.36 ms
Buffer.toString ascii string 77.68 ms/iter 12.9 (67.46 ms … 95.68 ms) 84.71 ms 95.68 ms 95.68 ms
Buffer.toString base64 string 825.53 µs/iter 1,211.3 (655.38 µs … 6.69 ms) 816.62 µs 3.07 ms 3.13 ms
Buffer.toString utf16 string 76.54 ms/iter 13.1 (66.9 ms … 85.26 ms) 83.63 ms 85.26 ms 85.26 ms
Buffer.toString hex string 38.56 ms/iter 25.9 (33.83 ms … 46.56 ms) 45.33 ms 46.56 ms 46.56 ms
```
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In the spec, a URL record has an associated "blob URL entry", which for
`blob:` URLs is populated during parsing to contain a reference to the
`Blob` object that backs that object URL. It is this blob URL entry that
the `fetch` API uses to resolve an object URL.
Therefore, since the `Request` constructor parses URL inputs, it will
have an associated blob URL entry which will be used when fetching, even
if the object URL has been revoked since the construction of the
`Request` object. (The `Request` constructor takes the URL as a string
and parses it, so the object URL must be live at the time it is called.)
This PR adds a new `blobFromObjectUrl` JS function (backed by a new
`op_blob_from_object_url` op) that, if the URL is a valid object URL,
returns a new `Blob` object whose parts are references to the same Rust
`BlobPart`s used by the original `Blob` object. It uses this function to
add a new `blobUrlEntry` field to inner requests, which will be `null`
or such a `Blob`, and then uses `Blob.prototype.stream()` as the
response's body. As a result of this, the `blob:` URL resolution from
`op_fetch` is now useless, and has been removed.
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