[clang] Reapply "[Clang] Fix dependent local class instantiation bugs" (PR #135914)

[Daniel Thornburgh via cfe-commits]

mysterymath wrote:

> @mysterymath In the meantime, can you please help us test the Fuchsia CI with this patch? I appreciate your help :)

We're not really set up to run the full Fuchsia CI with specific upstream patches, and it's a bit too flaky and expensive to be much good for that anyway. For now, it's better as post-submit than pre-submit, I'm afraid.

So long as this fixes the issue in the reproducer, and the LLVM tests pass, that should be good enough to go in.

https://github.com/llvm/llvm-project/pull/135914