[clang] [clang][ASTMatcher] Handle variable templates in `isInstantiated` and `isInTemplateInstantiation` matchers (PR #110666)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM! Sorry for the delayed review while I was out. No need to re-run the documentation macro because the public interfaces nor doc comments changed, and I think the existing doc comments are sufficient.

Do you need me to land the changes on your behalf?

https://github.com/llvm/llvm-project/pull/110666