Add arg_begin() and arg_end() to CallInst and InvokeInst; NFCI

 - This simplifies the CallSite class, arg_begin / arg_end are now
   simple wrapper getters.

 - In several places, we were creating CallSite instances solely to call
   arg_begin and arg_end.  With this change, that's no longer required.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@255226 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed