[llvm] [Support] Add format object for interleaved ranges (PR #135517)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Honestly `interleave` seems like the better name for this than `interleaved`... but I guess not a huge deal either way.

How would it look to migrate the existing uses of `interleave` to something like this instead fo introducing an alternative? (Probably have to do both so the migration isn't monolithic - but as a concept, is migrating a feasible/useful direction?)

https://github.com/llvm/llvm-project/pull/135517