[clang] [clang][ASTMatcher] Add matchers for CXXFoldExpr (PR #71245)

[Julian Schmidt via cfe-commits]

5chmidti wrote:

@EugeneZelenko sorry for the direct ping, but I know you are one of the people that are active with labels (thanks btw).
Could you please reapply the `clang` (or maybe the `clang:frontend` is a better fit) label to this pr? A now fixed issue with the pr subscriber notification action meant that the notification for groups did not happen for this pr.

https://github.com/llvm/llvm-project/pull/71245