MessageQueue: Change default queue size to 4096 KB

1024 KB was low enough that many users seem to hit it, which can lead to the
editor freezing.

The proper fixed as described in godotengine#35653 would be to implement a page allocator
to prevent this overflow, but as a stop-gap measure, we can increase the
default value to a more lenient 4096 KB which should be high enough for the
vast majority of use cases.

The default size can be brought down again if/when godotengine#35653 is properly fixed,
and if it's actually relevant from a memory point of view.

core/message_queue.h

@@ -38,8 +38,7 @@ class MessageQueue {
 	_THREAD_SAFE_CLASS_
 
 	enum {
-
-		DEFAULT_QUEUE_SIZE_KB = 1024
+		DEFAULT_QUEUE_SIZE_KB = 4096
 	};
 
 	enum {