Add Source Maps support

[Horcrux7]

To debug a Wasm module it can be helpful to see the original source code.

There is a feature request in the spec WebAssembly/design#1051

For a source map there must be custom section "sourceMappingURL" with the URL to the map.
This URL can relative if the wasm is load with WebAssembly.compileStreaming/instantiateStreaming. In the other case it relative to the baseURL of the web page. The URL can also be a data URI. Then it is inlined.

Currently Firefox support already displaying the source map.

There is a sample: https://github.com/yurydelendik/wasm-source-map-emscripten