[PM] Fix instcombine's analysis preservation in the new pass manager to

[PM] Fix instcombine's analysis preservation in the new pass manager to
cover domtree and alias analysis. These are the pretty clear analyses
that we would always want to survive this pass.

To make these survive, we also need to preserve the assumption cache.

Added a test that verifies the important bits of this preservation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292037 91177308-0d34-0410-b5e6-96231b3b80d8