[llvm-branch-commits] [BOLT] Add perf2bolt pre-aggregated profile output (PR #199465)

[Amir Ayupov via llvm-branch-commits]

https://github.com/aaupov created https://github.com/llvm/llvm-project/pull/199465

Add a pre-aggregated profile output format (`--profile-format=preagg`)
so perf.data can be pre-parsed/aggregated and used as input with -pa.

Supports branch and basic profiles, emits traces (T/R) and S records.

Currently only covers main binary, can be extended to cover multi-DSO.

Test Plan: Updated perf_test.test, added perf_brstack.test