The change adds support for triming and merging cold context when mergine CSSPGO profiles using llvm-profdata. This is similar to the context profile trimming in llvm-profgen, however the flexibility to trim cold context after profile is generated can be useful.
A bug fix is also included to make sure PSI thresholds are always calcuated before query.
clang-tidy: warning: 'auto &HotEntry' can be declared as 'const auto &HotEntry' [llvm-qualified-auto]
not useful