[Feature #18339] GVL Instrumentation API

Ref: https://bugs.ruby-lang.org/issues/18339

Design:

- This tries to minimize the overhead when no hook is registered.
  It should only incur an extra unsynchronized boolean check.
- The hook list is protected with a read-write lock as to cause
  contention when some hooks are registered.
- The hooks MUST be thread safe, and MUST NOT call into Ruby as they
  are executed outside the GVL.
- It's simply a noop on Windows.

API:

```
rb_internal_thread_event_hook_t * rb_internal_thread_add_event_hook(rb_internal_thread_event_callback callback, rb_event_flag_t internal_event, void *user_data);
bool rb_internal_thread_remove_event_hook(rb_internal_thread_event_hook_t * hook);
```

You can subscribe to 3 events:

  - READY: called right before attempting to acquire the GVL
  - RESUMED: called right after successfully acquiring the GVL
  - SUSPENDED: called right after releasing the GVL.

The hooks MUST be threadsafe, as they are executed outside of the GVL, they also MUST NOT call any Ruby API.

thread_win32.c

@@ -29,6 +29,18 @@ static volatile DWORD ruby_native_thread_key = TLS_OUT_OF_INDEXES;
 
 static int w32_wait_events(HANDLE *events, int count, DWORD timeout, rb_thread_t *th);
 
+rb_internal_thread_event_hook_t *
+rb_internal_thread_add_event_hook(rb_internal_thread_event_callback callback, rb_event_flag_t internal_event, void *user_data)
+{
+    // not implemented
+}
+
+bool
+rb_internal_thread_remove_event_hook(rb_internal_thread_event_hook_t * hook)
+{
+    // not implemented
+}
+
 RBIMPL_ATTR_NORETURN()
 static void
 w32_error(const char *func)