[clang] Regenerate AST matcher docs 📖

Summary:
The documentation seems to have been manually edited in https://reviews.llvm.org/rGa282bde69e375985edd4c371b79864f617380ad5.

This commit regenerates the documentation and commits the resulting diff.

Reviewers: benhamilton, mwyman

Reviewed By: mwyman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D61769

llvm-svn: 360545