ExpansionLoc was previously calculated incorrectly in the case of
nested macros expansions. In this diff we build the stack of expansions where the last one
is the actual expansion (in the source code) which should be used for grouping together
the edits. The definition of MacroArgUse is adjusted accordingly: now it's essentially the stack of expansions plus
the location of argument use inside the top-most macro.
This diff fixes https://bugs.llvm.org/show_bug.cgi?id=33447 .
Test plan: make check-all