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.
What will happen if these two flags are enabled for non-CSSPGO sample profile?