[docs] dump-ast-matchers removes const from Matcher args and handles template...

[docs] dump-ast-matchers removes const from Matcher args and handles template functions slightly better

Reviewers: aaron.ballman, gribozavr2, joerg

Reviewed By: aaron.ballman

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D75113