Drop old semaphore implementation

- Removed platform-specific implementations.
- Now all semaphores are in-object, unless they need to be conditionally created.
- Similarly to `Mutex`, provided a dummy implementation for when `NO_THREADS` is defined.
- Similarly to `Mutex`, methods are made `const` for easy use in such contexts.
- Language bindings updated: `wait()` and `post()` are now `void`.
- Language bindings updated: `try_wait()` added.

Bonus:
- Rewritten the `#ifdef` in `mutex.h` to meet the code style.

platform/uwp/os_uwp.cpp

@@ -140,7 +140,6 @@ void OS_UWP::initialize_core() {
 	//RedirectIOToConsole();
 
 	ThreadUWP::make_default();
-	SemaphoreWindows::make_default();
 	RWLockWindows::make_default();
 
 	FileAccess::make_default<FileAccessWindows>(FileAccess::ACCESS_RESOURCES);