[llvm] [ADT] Add DenseSet(llvm::from_t, Range) (PR #131832)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> Other people feel strongly otherwise?

I'm fine with that too, but I'm not entirely convinced that this is a better convention than a helper function or a 'static constructor function' like `DenseSet<Foo>::fromRange(...)`. Or put it differently, is it work aligning with C++ stuff that we are unlikely to adopt in the future?

https://github.com/llvm/llvm-project/pull/131832