[llvm-profdata] Improve profile supplementation

Current implementation promotes a non-cold function in the SampleFDO profile
into a hot function in the FDO profile. This is too aggressive. This patch
promotes a hot functions in the SampleFDO profile into a hot function, and a
warm function in SampleFDO into a warm function in FDO.

Differential Revision: https://reviews.llvm.org/D132601