[Diagnostics] Allow emitting analysis and missed remarks on functions

Summary:
Currently, only `OptimizationRemarks` can be emitted using a Function.
Add constructors to allow this for `OptimizationRemarksAnalysis` and
`OptimizationRemarkMissed` as well.

Reviewed By: jdoerfert thegameg

Differential Revision: https://reviews.llvm.org/D102784