[PM] Port domtree to the new pass manager (at last).

This adds the domtree analysis to the new pass manager. The analysis
returns the same DominatorTree result entity used by the old pass
manager and essentially all of the code is shared. We just have
different boilerplate for running and printing the analysis.

I've converted one test to run in both modes just to make sure this is
exercised while both are live in the tree.

llvm-svn: 225969