[PGO] Add a threshold for number of critical edges in PGO

[PGO] Add a threshold for number of critical edges in PGO

For some auto-generated sources, we have a huge number of critical
edges (like from switch statements). We have seen instance of 183777
critical edges in one function.

After we split the critical edges in PGO instrumentation/profile-use
pass, the CFG is so large that we have compiler time issues in
downstream passes (like in machine CSE and block placement). Here I
add a threshold to skip PGO if the number of critical edges are too
large.

The threshold is large enough so that it will not affect the majority
of PGO compilation.

Also sync the logic for skipping instrumentation and profile-use. I
think this is the correct thing to do.

Differential Revision: https://reviews.llvm.org/D137184