[BOLT][NFCI] Speedup BAT::writeMaps
For a large binary with BAT section of size 38 MB with ~170k maps,
reduces writeMaps time from 70s down to 1s.
The inefficiency was in the use of std::distance with std::map::iterator
which doesn't provide random access. Use sorted vector for lookups.
Test Plan: NFC
Reviewers: maksfb, rafaelauler, dcci, ayermolo
Reviewed By: maksfb
Pull Request: https://github.com/llvm/llvm-project/pull/112061
