[clang-query] Add non-exclusive output API

Summary:
Add granular options for AST dumping, text printing and diagnostics.

This makes it possible to

* Have both diag and dump active at once
* Extend the output with other queryable content in the future.

Reviewers: aaron.ballman, pcc, ioeric, ilya-biryukov, klimek, sammccall

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D52857

llvm-svn: 345522