Demangle Rust symbol names in wasm-decompile

[linkmauve]

For instance, ZN4hvif5shape5Shape5parse17ha264877da5eed17bE() should be something like hvif::shape::Shape::parse().

This issue is related to #1406, but specific to the symbols generated by rustc.

[majaha]

Just FYI, you can pipe through the tool rustfilt to do this! https://github.com/luser/rustfilt