[llvm] [BOLT] Add unit tests for pre-aggregated profile parsing (PR #192390)

[Paschalis Mpeis via llvm-commits]

https://github.com/paschalis-mpeis commented:

> I guess we are at the level of complexity for the parser where it needs dedicated unit tests.

Yeap, I don't know whether, in the future, we can better manage the boilerplate code.
On top of what was said, they can also help with understanding the code, eg show in which structure the textual profile ends up in.

https://github.com/llvm/llvm-project/pull/192390