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/cli/tools/fmt.rs b/cli/tools/fmt.rs
index 70d2bd639..f2fec9302 100644
--- a/cli/tools/fmt.rs
+++ b/cli/tools/fmt.rs
@@ -28,6 +28,7 @@ use deno_core::error::generic_error;
 use deno_core::error::AnyError;
 use deno_core::futures;
 use deno_core::parking_lot::Mutex;
+use deno_core::task::spawn_blocking;
 use log::debug;
 use log::info;
 use log::warn;
@@ -629,7 +630,7 @@ where
   let handles = file_paths.iter().map(|file_path| {
     let f = f.clone();
     let file_path = file_path.clone();
-    tokio::task::spawn_blocking(move || f(file_path))
+    spawn_blocking(move || f(file_path))
   });
   let join_results = futures::future::join_all(handles).await;