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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225094 91177308-0d34-0410-b5e6-96231b3b80d8
87df619177