[llvm] [Support][Casting] Add predicates for `isa*` functions (PR #83753)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> It'd probably be an issue for some callers, but we could make the actual `isa`, etc into functors so we don't need to introduce new names? Something like this: https://stackoverflow.com/questions/62928396/what-is-a-niebloid (not in this case to thwart overloading, but to make it easy to pass as functors)

I'm worried about the side effects, given that this is probably one of the most commonly used function across the whole project and downstream projects:
* Any code that explicitly specified the `From` template argument would **silently** break (the interpretation would change to another possible cast type)
* This disables ADL


https://github.com/llvm/llvm-project/pull/83753