This replaces GetAstMatcher with AddMatcher because cxxForRangeStmt is a StatementMatcher. addMatcher has multiple definitions (https://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder.html) and so this approach allows using the right addMatcher without writing per-call overloads.
To handle the `var`, I'm considering something like moving VarDecl logic into a VarMatcherBase so that I can just use CXXForRangeStmt's getLoopVariable. The problem is a for-range statement has multiple VarDecls, and getLoopVariable may be the easiest way to identify the real one.
This replaces the use of `isExpansionInMainFile` with instead taking the list of input files, and only touching them. This doesn't keep `isExpansionInMainFile` because it should be redundant, and as such it'd be easy to forget. Unless it starts being a performance issue, it's probably better to omit.
Jon Meow
