This allows removing it from `class_db.h`, significantly reducing the amount of files
that include it transitively.
Also includes some include cleanup in `control.h` and `rich_text_label.h` done while
ensure they don't depend on `callable_mp`.
Updated ObjectDBProfilerPanel::receive_snapshot to check if file exists, and make filename unique before writing, to avoid overwriting when multiple snapshots are made within same second.
Updated GameStateSnapshot to inherit from RefCounted, to be automatically deleted when reference count reaches zero, and removed GameStateSnapshotRef wrapper class.
A new tab is added to the debugger that can help profile a game's memory usage.
Specifically, this lets you save a snapshot of all the objects in a running
game's ObjectDB to disk. It then lets you view the snapshot and diff two
snapshots against each other. This is meant to work similarly to Chrome's
heap snapshot tool or Unity's memory profiler.
