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

[Jakub Kuderski via llvm-commits]

kuhar wrote:

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

`interleave` is already taken unless we nest this in a new namespace.

> 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?)

Yes, I want to migrate existing uses of `interleave` to this. We should be able to deprecate `interleave` eventually.

> Oh, and any precedent for this in the standard library or boost, etc? So we can pick a similar name/interface at least?

Yes! This is inspired by https://en.cppreference.com/w/cpp/io/manip/quoted -- the naming is similar on purpose. I'm not aware of anything for ranges though.

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