[BOLT] Introduce non-LBR mode

Summary:
Add support to read profiles collected without LBR. This
involves adapting our data aggregator perf2bolt and adding support
in llvm-bolt itself to read this data.

This patch also introduces different options to convert basic block
execution count to edge count, so BOLT can operate with its regular
algorithms to perform basic block layout. The most successful approach
is the default one.

(cherry picked from FBD5664735)