[clang] [clang-tools-extra] [lldb] [clang] Reland: fix getTemplateInstantiationArgs (PR #207825)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@davidstone the patch touches one of the most painful part of clang, this difficulty is not merely due to a failure to split the work into smaller patches, as there have been similar attempts in the past that were eventually abandoned after multiple reverts. Template in-production uses are almost unpredictable and thus we can't have sufficient test coverage.


https://github.com/llvm/llvm-project/pull/207825