[JumpThreading] Preserve profile metadata during select unfolding, take 2

Jump threading can replace select and unconditional branch with
conditional branch, but when doing so loses profile information.

This destructive transform can eventually lead to a performance
degradation due to folding of branches in
shouldFoldCondBranchesToCommonDestination as branch probabilities
are no longer known.

The first version was reverted due to assert caused by i32 overflow,
fixed in this version.

Patch by Roman Paukner!

Differential Revision: https://reviews.llvm.org/D138132
Reviewed By: mkazantsev