wasm-emscripten-finalize doesn't preserve sourcesContent

[verhovsky]

If you can't host the files for your source map, you can put their contents in the sourcesContent field of your source map JSON file https://tc39.es/source-map/#sourcescontent

When emscripten runs wasm-emscripten-finalize on a source map file that has that field set

https://github.com/emscripten-core/emscripten/blob/cf0ec7a4426203d76f958216d14ad9f4513d8481/tools/emscripten.py#L488-L491

wasm-emscripten-finalize removes it.

emscripten-core/emscripten#22190