Add support for Rust v0 symbol mangling scheme

[cerisier]

Rust has defined its own symbol mangling scheme (https://rust-lang.github.io/rfcs/2603-rust-symbol-name-mangling-v0.html) which is currently not supported since it differs completely from the C++ name mangling scheme speedscope already support.

I can see that the C++ demangling support was taken from what seems like a pre WASM C++/Javascript transpilation process but not sure what?

If Rust demangling support makes sense for speedscope, what would be the best way to add support for it ?
Would you be open to loading WASM modules for demangling support ?

That way we could just use the official demangle from https://github.com/rust-lang/rustc-demangle
We could even do the same for C++ with abi::__cxa_demangle from cxxabi.h.