Implement Mangling of GraphIR Terms

[CodaFi]

Part of #99: We must mangle the full module name into the name of a term as well as normalize Arbitrary Unicode Garbage in symbol names. The GIRWriter can then be updated to account for this.

[CodaFi]

We should never need to mangle the type of a declaration into the symbol (I suspect we can figure this out at runtime from the type metadata)

[harlanhaskins]

What about specialized functions?

[CodaFi]

We can mangle the fact that we specialized parameters, but I think specializations will be internal to the calling module so we can come up with any old naming scheme.

[harlanhaskins]

If we do this, we should implement demangling in the runtime, for debugging and crash tracing purposes.