It is only used in the client, I think it makes sense to move it there, or to remove it altogether.
I think I'd keep it in the client for now, to disambiguate things with different names in the tests.
I didn't realize that you're including files from within lib. That's not ideal. You should add a pre-commit that moves the *.inc files over to include/AST (and marks them as textual in Clang's module.modulemap). Then you should include them using the clang/AST path.
I tried moving StmtDataCollectors.inc to and adding
It might make sense to tablegen it like the other .inc files.