Investigate performance impact of debuginfo typename generation

[michaelwoerister]

The code generating type names for debuginfo does not seem to do any kind of caching of repeatedly occurring string segments (e.g. path prefixes and type renderings). Given that type names can get very long when generics are involved it's worth investigating how much time the compiler spends doing redundant work here.

[jyn514]

#84873 (comment) is also somewhat related, the names getting passed into llvm can get very long, especially for generators