[Attributor] Use `changeUseAfterManifest` in AAValueSimplify manifest

Summary: This patch makes `AAValueSimplify` use `changeUsesAfterManifest` in `manifest`. This will invoke simple folding after the manifest.

Reviewers: jdoerfert, sstefan1

Reviewed By: jdoerfert

Subscribers: hiraditya, arphaman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71972