Some alias analysis fixes (#25425)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25425
1. Properly invalidate memory locations when we change the points-to
set.
2. Don't build a new indexToElementMap in toString(), just use
`MemoryDag::fromIndex`
3. Fix transitive wildcard assignment
Test Plan: Imported from OSS
Differential Revision: D17126402
Pulled By: suo
fbshipit-source-id: cbd99027d2e78fd333dbf030172d3b7ac4df8349
