[clang] [clang-tools-extra] [clang-query] Allow for trailing comma in matchers (PR #148018)

[Remy Farley via cfe-commits]

one-d-wide wrote:

I don't think this is much of an issue. Once you attempt to interpret a query with trailing comma in it as C++ code, a compiler (or even an LSP) will usually emit a (mostly) unambiguous error, which should be trivial to correct. And that's it. Existing queries, including ones ported back from C++, are unaffected.

I see this feature as only helpful during the development of a query, smoothing the experience by, for example, allowing to conveniently comment query arguments out (which also done in a way incompatible with C++ btw). 

In which case getting an error is rather annoying, since matcher arguments act more like parameters in a C++ initializer list (where trailing comma is actually allowed), rather than positional arguments in a function.

Updated release notes.

https://github.com/llvm/llvm-project/pull/148018