[PM] Port LowerExpectIntrinsic to the new pass manager.

This just lifts the logic into a static helper function, sinks the
legacy pass to be a trivial wrapper of that helper fuction, and adds
a trivial wrapper for the new PM as well. Not much to see here.

I switched a test case to run in both modes, but we have to strip the
dead prototypes separately as that pass isn't in the new pass manager
(yet).

llvm-svn: 226999