[PM] Lift the majority of the template boilerplate used to implement the

concept-based polymorphism in the pass manager to a separate header.

I got feedback from someone reading the code and trying to use it that
this was really making it hard to dive in and start using these APIs and
that makes a lot of sense.

This only requires a moderate amount of gymnastics to separate in this
way, namely rinsing the PreservedAnalysis object through a template
argument in a few places so that it is dependent and we only examine it
on instantiation.

llvm-svn: 225094