Track the source location of the dot or arrow operator in a MemberExpr.

include/clang/AST/Expr.h

lib/AST/Expr.cpp

lib/Frontend/Rewrite/RewriteModernObjC.cpp

lib/Frontend/Rewrite/RewriteObjC.cpp

lib/Sema/SemaExprCXX.cpp

lib/Sema/SemaExprMember.cpp

lib/Sema/SemaOverload.cpp

lib/Sema/TreeTransform.h

lib/Serialization/ASTReaderStmt.cpp

lib/Serialization/ASTWriterStmt.cpp

unittests/AST/SourceLocationTest.cpp