Add support for .bind("foo") expressions on the dynamic matchers.

Summary: Add support on the parser, registry, and DynTypedMatcher for binding IDs dynamically.

Reviewers: klimek

CC: cfe-commits, revane

Differential Revision: http://llvm-reviews.chandlerc.com/D911

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183144 91177308-0d34-0410-b5e6-96231b3b80d8