Use --target web in wasm-bindgen and file-loader for WASM files,
allowing wasm-bindgen's built-in fallback from
WebAssembly.instantiateStreaming to instantiate.
file-loader spits out the WASM file directly in the output folder,
and imports will resolve to the URL, so that we can load the file
directly, avoiding webpack's built-in wasm loaders.
This allows Ruffle to function on web servers even if they serve
WASM files with the incorrect MIME type, fixing one of our biggest
support requests (#400, #1458). There is some performance impact
on loading with the fallback, but this is preferable to not
working at all.
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