fix: takes too much time to load singleton

[Ark2000]

	# Enable required time measurements to display CPU/GPU frame time information.
	RenderingServer.viewport_set_measure_render_time(get_viewport().get_viewport_rid(), true)
	update_information_label()
	update_settings_label()

the above code is very time consuming which will block the main thread and increase startup time by about three to four seconds, so I put them in a separate thread to avoid the block.

[Calinou]

I'll test this locally when I get home.

In my experience, the biggest culprit by far is getting the graphics driver version, which is very slow for some reason. I suggest using a C++ profiler on a debug build of the engine to determine why.

@myaaaaaaaaa Do you know a better way to do this?

[myaaaaaaaaa]

I generally diagnose performance problems like these using very advanced techniques such as putting printf(timestamp)s everywhere, commenting out lines of code until something changes, or Ctrl+C-ing in gdb once it reaches time-consuming code so that backtraces show likely culprits 🙃

[Calinou]

Merged manually with c7f463b, which also displays loading text and prevents a warning from being printed by calling wait_to_finish() on the thread instance.

Thanks!