[DSE,MemorySSA] Use BatchAA for AA queries.

We can use BatchAA to avoid some repeated AA queries. We only remove
stores, so I think we will get away with using a single BatchAA instance
for the complete run.

The changes in AliasAnalysis.h mirror the changes in D85583.

The change improves compile-time by roughly 1%.
http://llvm-compile-time-tracker.com/compare.php?from=67ad786353dfcc7633c65de11601d7823746378e&to=10529e5b43809808e8c198f88fffd8f756554e45&stat=instructions

This is part of the patches to bring down compile-time to the level
referenced in
http://lists.llvm.org/pipermail/llvm-dev/2020-August/144417.html

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D86275