Modernize Thread

- Based on C++11's `thread` and `thread_local`
- No more need to allocate-deallocate or check for null
- No pointer anymore, just a member variable
- Platform-specific implementations no longer needed (except for the few cases of non-portable functions)
- Simpler for `NO_THREADS`
- Thread ids are now the same across platforms (main is 1; others follow)

servers/audio/effects/audio_effect_record.cpp

@@ -118,7 +118,7 @@ void AudioEffectRecordInstance::init() {
 #ifdef NO_THREADS
 	AudioServer::get_singleton()->add_update_callback(&AudioEffectRecordInstance::_update, this);
 #else
-	io_thread = Thread::create(_thread_callback, this);
+	io_thread.start(_thread_callback, this);
 #endif
 }
 
@@ -126,9 +126,7 @@ void AudioEffectRecordInstance::finish() {
 #ifdef NO_THREADS
 	AudioServer::get_singleton()->remove_update_callback(&AudioEffectRecordInstance::_update, this);
 #else
-	if (thread_active) {
-		Thread::wait_to_finish(io_thread);
-	}
+	io_thread.wait_to_finish();
 #endif
 }
 

servers/audio/effects/audio_effect_record.h

@@ -48,7 +48,7 @@ class AudioEffectRecordInstance : public AudioEffectInstance {
 	Ref<AudioEffectRecord> base;
 
 	bool is_recording;
-	Thread *io_thread;
+	Thread io_thread;
 	bool thread_active = false;
 
 	Vector<AudioFrame> ring_buffer;