refactor(core): bake single-thread assumptions into spawn/spawn_blocking (#19056)

Partially supersedes #19016.

This migrates `spawn` and `spawn_blocking` to `deno_core`, and removes
the requirement for `spawn` tasks to be `Send` given our single-threaded
executor.

While we don't need to technically do anything w/`spawn_blocking`, this
allows us to have a single `JoinHandle` type that works for both cases,
and allows us to more easily experiment with alternative
`spawn_blocking` implementations that do not require tokio (ie: rayon).

Async ops (+~35%):

Before: 

```
time 1310 ms rate 763358
time 1267 ms rate 789265
time 1259 ms rate 794281
time 1266 ms rate 789889
```

After:

```
time 956 ms rate 1046025
time 954 ms rate 1048218
time 924 ms rate 1082251
time 920 ms rate 1086956
```

HTTP serve (+~4.4%):

Before:

```
Running 10s test @ http://localhost:4500
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    68.78us   19.77us   1.43ms   86.84%
    Req/Sec    68.78k     5.00k   73.84k    91.58%
  1381833 requests in 10.10s, 167.36MB read
Requests/sec: 136823.29
Transfer/sec:     16.57MB
```

After:

```
Running 10s test @ http://localhost:4500
  2 threads and 10 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    63.12us   17.43us   1.11ms   85.13%
    Req/Sec    71.82k     3.71k   77.02k    79.21%
  1443195 requests in 10.10s, 174.79MB read
Requests/sec: 142921.99
Transfer/sec:     17.31MB
```

Suggested-By: alice@ryhl.io
Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/ext/crypto/lib.rs b/ext/crypto/lib.rs
index f481f97f6..05349bf68 100644
--- a/ext/crypto/lib.rs
+++ b/ext/crypto/lib.rs
@@ -10,6 +10,7 @@ use deno_core::error::type_error;
 use deno_core::error::AnyError;
 use deno_core::op;
 
+use deno_core::task::spawn_blocking;
 use deno_core::OpState;
 use deno_core::ZeroCopyBuf;
 use serde::Deserialize;
@@ -601,7 +602,7 @@ pub async fn op_crypto_subtle_digest(
   algorithm: CryptoHash,
   data: ZeroCopyBuf,
 ) -> Result<ZeroCopyBuf, AnyError> {
-  let output = tokio::task::spawn_blocking(move || {
+  let output = spawn_blocking(move || {
     digest::digest(algorithm.into(), &data)
       .as_ref()
       .to_vec()