Emscripten improvements

[BinBashBanana]

Description

• Canvas is now resized to the correct size, image should no longer be blurry (this may not work in safari)
• More exported functions added, fixed a bug in cheat manager
  • Added RELOAD_CONFIG command event
• Added library_platform_emscripten.js to manage more platform functions without using EM_ASM/EM_JS
• Added a config option to ignore missing assets (currently ozone only) - this enables drawing the fancy cursor
• Added touch input support (up to 32 touches?)
• Fixed FP/sRGB FBO detection/support which caused some shader pipelines to break in GLES3, and enables more in GLES2
• Fixed up emscripten makefile, build script, and web player

Reviewers

@LibretroAdmin @m4xw @hunterk

[m4xw]

Please note that the .bc -> .a change is a change that occured in recent toolchain versions and we would need to change all core makefiles on libretro side

[LibretroAdmin]

Failing checks are unrelated to this PR. This will likely resolve itself as you push a new commit to this PR.

[LibretroAdmin]

@BinBashBanana Why was this closed?

[BinBashBanana]

Rebasing again, I didn't realize it would auto-close

[BinBashBanana]

Android build failure seems unrelated?

[BinBashBanana]

Just a moment, I need to go get lunch :D

[LibretroAdmin]

Seems like the only build error now is Emscripten

[BinBashBanana]

Ready and tested with dummy, nestopia, snes9x, and mupen64plus_next (patched).

[BinBashBanana]

If possible, emscripten on the buildbot should be updated (I'm using 3.1.74) - this enables the INITIAL_HEAP setting which gives better control over memory.

[BinBashBanana]

Anything else that needs to be changed before this is merged?

[RobLoach]

Overall seems like good changes. Thanks for keeping emscripten build going.

[BinBashBanana]

One more rebase. Just fixed 3c3611a as well (#15559 needed "override")