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

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic commented:

I'm a little hesitant to endorse this.  Blocks were originally designed in the context of ObjC; we've dragged them into C++ to the point that they basically work, but that's mostly for the sake of ObjC interop, not for use in pure C++.  We should encourage people to use C++ lambdas for native C++ code.

CC @ahatanak 

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