Debugging the Rust Code in the Web

[CryZe]

This is basically just a tracking issue for eventually supporting stepping through the Rust code in the browser. I already kind of got it to work:

However it seems like wasm-bindgen, wasm-opt and other tools (possibly webpack too) break it, because they don't preserve the debugging information, so this is blocked until they make further progress.

There's also this: https://github.com/yurydelendik/wtmaps-utils

This is the only real upstream tracking issue that I found: https://github.com/rustwasm/walrus/issues/67