[clang] [clang][transformer] Allow usage of applyFirst with rewriteDescendants (PR #117658)

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SherAndrei wrote:

> Can you expand on your concern about the clash?

The clash is happening in `NodesMap`. See, 
1. the matcher which is associated with `rewriteDescendants` gets "Tag0",
2. tags for matchers from `applyfirst` are shifted, they get "Tag1", ...
3. that is why `transformer::detail::findSelectedCase` selects incorrect `Tag` from `NodesMap` (this also leads to error "ID not bound", for expected bound ID from other matcher)

Do you want for me to update the description of the commit?

https://github.com/llvm/llvm-project/pull/117658