[PM] Port JumpThreading to the new PM

This follows the approach in r263208 (for GVN) pretty closely:
- move the bulk of the body of the function to the new PM class.
- expose a runImpl method on the new-PM class that takes the IRUnitT and
  pointers/references to any analyses and use that to implement the
  old-PM class.
- use a private namespace in the header for stuff that used to be file
  scope

llvm-svn: 272597