[clang] [clang][Sema] support block pointers as non-type template parameters (PR #191694)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt commented:

(ugh, I didn't push this PR feedback so it was just sitting in pending sorry)
Could we add tests for auto NTTPs, and template argument deduction?

https://github.com/llvm/llvm-project/pull/191694