[ModRef] Move ModRefInfo and FunctionModRefBehavior into IR (NFC)

This is in preparation for
https://discourse.llvm.org/t/rfc-unify-memory-effect-attributes/65579.
FunctionModRefBehavior will be used by attributes, and as such has
to be available in IR, not just Analysis.

Differential Revision: https://reviews.llvm.org/D135589