[llvm] [PatternMatch][VPlan] Add std::function match overload. NFCI (PR #146374)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > Reverse ping. Seems like a great innovation/improvement!
> 
> @artagnon Thanks for landing the PatternMatch part of this. Do you want to take over the VPlan part of this?

Sure, will do.

https://github.com/llvm/llvm-project/pull/146374