Use ExprMutationAnalyzer in performance-for-range-copy

Summary:
This gives better coverage to the check as ExprMutationAnalyzer is more
accurate comparing to isOnlyUsedAsConst.

Majority of wins come from const usage of member field, e.g.:
for (auto widget : container) { // copy of loop variable
  if (widget.type == BUTTON) { // const usage only recognized by ExprMutationAnalyzer
    // ...
  }
}

Reviewers: george.karpenkov

Subscribers: a.sidorin, cfe-commits

Differential Revision: https://reviews.llvm.org/D48854

llvm-svn: 336737