[CSSPGO] Enable loading MD5 CS profile.

Adding the compiler support of MD5 CS profile based on pervious context split work D107299. A MD5 CS profile is about 40% smaller than the string-based extbinary profile. As a result, the compilation is 15% faster.

There are a few conversion from real names to md5 names that have been made on the sample loader and context tracker side to get it work.

Reviewed By: wenlei, wmi

Differential Revision: https://reviews.llvm.org/D108342