Support threads in the script debugger

* This implementation adds threads on the side of the client (script debugger).
* Some functions of the debugger are optimized.
* The profile is also now thread safe using atomics.
* The editor can switch between multiple threads when debugging.

This PR adds threaded support for the script language debugger. Every thread has its own thread local data and it will connect to the debugger using multiple thread IDs.
This means that, now, the editor can receive multiple threads entering debug mode at the same time.

core/debugger/debugger_marshalls.h

@@ -38,6 +38,7 @@ struct DebuggerMarshalls {
 		String name;
 		Variant value;
 		int type = -1;
+		int var_type = -1;
 
 		Array serialize(int max_size = 1 << 20); // 1 MiB default.
 		bool deserialize(const Array &p_arr);