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

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> Wouldn't using an explicit ctor avoid that? That's what SmallVector does.

I think we guard against incompatible element types with the arrayref version but not against different small sizes with the `SmallVectorImpl` one: https://github.com/llvm/llvm-project/blob/adcaf1769dea988e13615ef088ff22629966de00/llvm/include/llvm/ADT/SmallVector.h#L1230-L1254 . For sets this would be difficult to controll without introducing explicit overloads for patterns prone to being misused. This is fixable, but I think that `from_range` is simpler/safer in comparison.

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