[clang] [clang-tools-extra] [lldb] [clang] Reland: fix getTemplateInstantiationArgs (PR #208285)

[Hans Wennborg via cfe-commits]

zmodem wrote:

Thanks for the explanation.

I'm about to go on vacation, otherwise I'd offer pre-testing this on Chromium before the next reland.

I don't know if it would be possible for @petrhosek or @eaeltsin to try it out on their codebases, but that could be a way to discover more issues without "testing in production". Or maybe just give clang-vendors some heads up next time?

https://github.com/llvm/llvm-project/pull/208285