[rcore][RGFW] Add new backend option: PLATFORM_WEB_RGFW

[ColleagueRiley]

This is a WIP pull request.

[ColleagueRiley]

Issues thus far:

• Fullscreen toggle causing screen to go black

• more testing has to be done

[raysan5]

@ColleagueRiley Thank you very much for working on this new platform backend! Exiting to have a GLFW alternative for PLATFORM_WEB! Keep up the great work!

[orcmid]

@raysan5 @ColleagueRiley
Is it still the raylib practice not to modify externals since the latest ones upstream are included at each release?

Is an exception being made to maintain RGFW.h under raylib?

Musing: The platforms changes setup is intriguing. I am not quite clear how one deals with maintenance and confirmation across them, especially with raylib changes that impact rcore.c. Not my problem, but something that catches my eye.

[ColleagueRiley]

@raysan5 The only remaining issue with the web platform is the fullscreen toggle.