Build system madness

[kapi1525]

TLDR: Decided to move the sdk to a meson subproject. This allows me to not worry about overwriting sdk variables in the ext meson.build file.

This also includes a lot of other build system related improvements/changes:

• Workarrouds to get wasm compiling on windows
• Replaced one stupid hack with a less stupid workarround for Ext.wasm file being installed with meson install
• Directly run esbuild without relying on npm scripts
• MMF2Exts commit hash gets read from file
• Added detection for official linux 7zip
• Android java ext wrapper, gets generated at configure time, from a template.
• Ported over darkedif feature detection (pausable, display type, debugger etc), prolly less fancy compared to the original but it works
• Probably more changes I forgot about...