[llvm] [NFC][InstrProf]Factor out getCanonicalName to compute the canonical name given a pgo name. (PR #81547)

[Mingming Liu via llvm-commits]

minglotus-6 wrote:

I read this PR again and made a [change](https://github.com/llvm/llvm-project/pull/81547/commits/795aa98c178bb534850a3489e8ad81c2460f526a) to use `SmallVector` rather than `StringSet`. 

https://github.com/llvm/llvm-project/pull/81547