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>

4 files changed, 8 insertions, 4 deletions

diff --git a/ext/crypto/decrypt.rs b/ext/crypto/decrypt.rs
index 6c4d5b6ba..fc54fe818 100644
--- a/ext/crypto/decrypt.rs
+++ b/ext/crypto/decrypt.rs
@@ -20,6 +20,7 @@ use deno_core::error::custom_error;
 use deno_core::error::type_error;
 use deno_core::error::AnyError;
 use deno_core::op;
+use deno_core::task::spawn_blocking;
 use deno_core::ZeroCopyBuf;
 use rsa::pkcs1::DecodeRsaPrivateKey;
 use rsa::PaddingScheme;
@@ -98,7 +99,7 @@ pub async fn op_crypto_decrypt(
       tag_length,
     } => decrypt_aes_gcm(key, length, tag_length, iv, additional_data, &data),
   };
-  let buf = tokio::task::spawn_blocking(fun).await.unwrap()?;
+  let buf = spawn_blocking(fun).await.unwrap()?;
   Ok(buf.into())
 }
 
diff --git a/ext/crypto/encrypt.rs b/ext/crypto/encrypt.rs
index f34e0cbc6..2831ca0f4 100644
--- a/ext/crypto/encrypt.rs
+++ b/ext/crypto/encrypt.rs
@@ -19,6 +19,7 @@ use ctr::Ctr64BE;
 use deno_core::error::type_error;
 use deno_core::error::AnyError;
 use deno_core::op;
+use deno_core::task::spawn_blocking;
 use deno_core::ZeroCopyBuf;
 use rand::rngs::OsRng;
 use rsa::pkcs1::DecodeRsaPublicKey;
@@ -99,7 +100,7 @@ pub async fn op_crypto_encrypt(
       key_length,
     } => encrypt_aes_ctr(key, key_length, &counter, ctr_length, &data),
   };
-  let buf = tokio::task::spawn_blocking(fun).await.unwrap()?;
+  let buf = spawn_blocking(fun).await.unwrap()?;
   Ok(buf.into())
 }
 
diff --git a/ext/crypto/generate_key.rs b/ext/crypto/generate_key.rs
index 2a9452c43..426c61376 100644
--- a/ext/crypto/generate_key.rs
+++ b/ext/crypto/generate_key.rs
@@ -2,6 +2,7 @@
 
 use deno_core::error::AnyError;
 use deno_core::op;
+use deno_core::task::spawn_blocking;
 use deno_core::ZeroCopyBuf;
 use elliptic_curve::rand_core::OsRng;
 use num_traits::FromPrimitive;
@@ -56,7 +57,7 @@ pub async fn op_crypto_generate_key(
       generate_key_hmac(hash, length)
     }
   };
-  let buf = tokio::task::spawn_blocking(fun).await.unwrap()?;
+  let buf = spawn_blocking(fun).await.unwrap()?;
   Ok(buf.into())
 }
 
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()