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>

3 files changed, 14 insertions, 8 deletions

diff --git a/runtime/inspector_server.rs b/runtime/inspector_server.rs
index 25d0d796c..1a6706896 100644
--- a/runtime/inspector_server.rs
+++ b/runtime/inspector_server.rs
@@ -15,6 +15,7 @@ use deno_core::futures::task::Poll;
 use deno_core::serde_json;
 use deno_core::serde_json::json;
 use deno_core::serde_json::Value;
+use deno_core::task::spawn;
 use deno_core::InspectorMsg;
 use deno_core::InspectorSessionProxy;
 use deno_core::JsRuntime;
@@ -109,7 +110,7 @@ where
   Fut::Output: 'static,
 {
   fn execute(&self, fut: Fut) {
-    tokio::task::spawn_local(fut);
+    deno_core::task::spawn(fut);
   }
 }
 
@@ -160,7 +161,7 @@ fn handle_ws_request(
 
   // spawn a task that will wait for websocket connection and then pump messages between
   // the socket and inspector proxy
-  tokio::task::spawn_local(async move {
+  spawn(async move {
     let websocket = if let Ok(w) = fut.await {
       w
     } else {
diff --git a/runtime/tokio_util.rs b/runtime/tokio_util.rs
index a4db5e33f..ce6ef305f 100644
--- a/runtime/tokio_util.rs
+++ b/runtime/tokio_util.rs
@@ -1,5 +1,7 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
 
+use deno_core::task::MaskFutureAsSend;
+
 pub fn create_basic_runtime() -> tokio::runtime::Runtime {
   tokio::runtime::Builder::new_current_thread()
     .enable_io()
@@ -14,11 +16,14 @@ pub fn create_basic_runtime() -> tokio::runtime::Runtime {
     .unwrap()
 }
 
-pub fn run_local<F, R>(future: F) -> R
+pub fn create_and_run_current_thread<F, R>(future: F) -> R
 where
-  F: std::future::Future<Output = R>,
+  F: std::future::Future<Output = R> + 'static,
+  R: Send + 'static,
 {
   let rt = create_basic_runtime();
-  let local = tokio::task::LocalSet::new();
-  local.block_on(&rt, future)
+  // SAFETY: this this is guaranteed to be running on a current-thread executor
+  let future = unsafe { MaskFutureAsSend::new(future) };
+  let join_handle = rt.spawn(future);
+  rt.block_on(join_handle).unwrap().into_inner()
 }
diff --git a/runtime/web_worker.rs b/runtime/web_worker.rs
index d8c881ab7..01262abcf 100644
--- a/runtime/web_worker.rs
+++ b/runtime/web_worker.rs
@@ -3,7 +3,7 @@ use crate::colors;
 use crate::inspector_server::InspectorServer;
 use crate::ops;
 use crate::permissions::PermissionsContainer;
-use crate::tokio_util::run_local;
+use crate::tokio_util::create_and_run_current_thread;
 use crate::worker::FormatJsErrorFn;
 use crate::BootstrapOptions;
 use deno_broadcast_channel::InMemoryBroadcastChannel;
@@ -838,5 +838,5 @@ pub fn run_web_worker(
     debug!("Worker thread shuts down {}", &name);
     result
   };
-  run_local(fut)
+  create_and_run_current_thread(fut)
 }