Use ASTDumper to dump the AST from clang-query
This way, the output is not limited by the various API differences
between the dump() member functions. For example, all dumps are now in
color, while that used to be the case only for Decls and Stmts, but not
Additionally, while DynTypedNode::dump (which was used up to now) was
limited to dumping only Decls, Stmts and Types, this makes clang-query
support everything ASTNodeTraverser supports.
Differential Revision: https://reviews.llvm.org/D62056