[wasm] move emsdk setup from runtime to emsdk tooling

[lewing]

Right now src/mono/mono.proj has complicated logic to use the emsdk packages to build runtime, that setup logic should be moved to emsdk and used where do similar things (like dotnet/icu)

see #105437 for an example

• emscripten config file
• Linux/Windows scripts emsdk_env*

[lewing]

tis is infrastructure and not blocking so I'm moving to 10