WIP: Support Qt for WebAssembly

[Vogtinator]

• Needs better platform integration (file management and settings)
• Must not break other platforms
• Fix caching of emsdk libraries in the GH build
• On Firefox on Android, the screen is drawn too large. I suppose the condition for iOS in qtframebuffer.cpp needs to be extended

[Vogtinator]

Demo deployed at https://nspire-emus.github.io/firebird/wasm

[Vogtinator]

• Fix caching of emsdk libraries in the GH build

Apparently that's because setup-emsdk behaves differently if the cache was found. If it's not found, it'll install emsdk into emsdk-main and create a cache in emsdk-cache. The system libs end up in emsdk-main in those builds, but only emsdk-cache is cached. If the cache is found, it uses emsdk-cache as emsdk location and build system libs inside that directory.

[Vogtinator]

Fix caching of emsdk libraries in the GH build

Fixed by running emsdk manually instead of using the setup-emsdk action

[Vogtinator]

-O3 -flto is not noticably faster compared to the default (-O3 for object files, -O2 for linking), but it takes twice as long to build.

[MumflrFumperdink]

I got persistent file management and offline access once loaded on https://github.com/MumflrFumperdink/firebird-updated-fork/tree/emscriptenjit. Try live version on https://mumflrfumperdink.github.io/firebird-updated-fork/firebird-emu.html