[BOLT] improvements for CFG construction

Summary:
Some improvements for CFG construction:
- getting rid of fallthrough-inferrence, as this is already
done DataAggregator;
- adjusting block counts for blocks with non-zero outgoing edges
to make sure they're not outlined;
- making sure that all functions (including non-simple ones) are
reordered and placed in the hot section.

The main goal of the diff is to make sure that constructed CFG graphs
exactly correspond to the input profile data.

(cherry picked from FBD7323205)