[CallSite removal] Port `IndirectCallSiteVisitor` to use `CallBase` and
update client code.

Also rename it to use the more generic term `call` instead of something
that could be confused with a praticular type.

Differential Revision: https://reviews.llvm.org/D56183

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350508 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed