[llvm] [MCA] Enable customization of individual instructions (PR #155420)

[Roman Belenov via llvm-commits]

r-belenov wrote:

> for a given Instrument, parse the Instrument::Data when the Instrument::Desc is equal to "LLVM-MCA-LATENCY:" 
It's possible to move the parsing logic to InstrumentManager, but we still need to keep parsed latency value (and the fact that it should be applied) for each region. We cant just keep the strings and do the parsing in the callbacks called from InstrBuilder, but that looks too expensive for me (especially in case MCA is used as a library and latency already comes in numeric form from some external source, so no parsing is required).

https://github.com/llvm/llvm-project/pull/155420