[CHR] Add a threshold for the code duplication

ControlHeightReduction (CHR) clones the code region to reduce the
branches in the hot code path. The number of clones is linear to the
depth of the region.

Currently it does not have control over the code size increase. We are
seeing one ~9000 BB functions get expanded to ~250000 BBs, an 25x
increase. This creates a big compile time issue for the downstream
optimizations.

This patch adds a cap for number of clones for one region.

Differential Revision: https://reviews.llvm.org/D138333