[clang] [clang] Track function template instantiation from definition (PR #110387)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

Thanks for taking another look at it.

My main concern is that changes in `getTemplateInstantiationArgs()` would conflict with @sdkrystian's recent work, so if these changes are necessary, I suggest we merge this one after the refactoring patch lands, WDYT? 

https://github.com/llvm/llvm-project/pull/110387