[clang] [clang] Fix TemplateInstantiator crash transforming loop hint argument (PR #172289)

[Erich Keane via cfe-commits]

erichkeane wrote:

> @erichkeane You already approved this PR, but not the additional changes that I did following your comments. To move forward, I would pre-commit (using a separate PR with the "skip-precommit-approval" label) the changes from commit [7fd8afd](https://github.com/llvm/llvm-project/commit/7fd8afdbcca87ce35e7ada286aa9cc4fa0f411be) (=independent fix of test patterns) and then rebase and merge this PR with the additional changes that I still did since your approval (=release note, additional code comment, extra test case). Would that be OK for you? Of course, feel free to raise any comments that you may still have.

I just did a review of the things you pushed since I reviewed, feel free to just merge the whole thing. 

https://github.com/llvm/llvm-project/pull/172289