Implement P2210R2 Superior String Splitting

[miscco]

This implements the first part of P2210R2 renaming split_view to lazy_split_view

Works towards #1980.

[StephanTLavavej]

@miscco - Are you still working on resolving @timsong-cpp's comments, or were they resolved in the recent commits? Just wondering whether this should move to Initial Review again. 😺

[miscco]

@miscco - Are you still working on resolving @timsong-cpp's comments, or were they resolved in the recent commits? Just wondering whether this should move to Initial Review again. 😺

Actually this is something that I would want to get @CaseyCarter's opinion on. As far as I remember his analysis was that we do not need to do anything related to P2281 and if we change something here I would want to be sure we change it consistently everywhere

[miscco]

@CaseyCarter I would also suggest to move this to a follow up. As far as I can tell there are two things we need to do

1. Improve the perfect forwarding for the adaptors
2. Iplement decay-copy for split_view and lazy_split_view

Given that those are non trivial changes (and I currently do not have that much capacity for delicate tasks) I feel it is better to extract them into a follow up.

[StephanTLavavej]

Thanks! I'll push changes to address my feedback (they were all localized).

[miscco]

Thanks a lot for the review and the fixes 😸

[StephanTLavavej]

I'm mirroring this to an MSVC-internal PR - please notify me if any further changes are pushed.

[StephanTLavavej]

"Thanks", "For", "Implementing", "This", "C++20", "Defect", "Report" 😸