US 61-126 32.11 [re.iter], 26.7.14 [range.join] Handle stashing iterators

[wg21bot]

join_view can’t handle stashing iterators, which makes such code break in unexpected ways. Range adaptors need to just work.
Also regex_iterator lies about its iterator_category in a way that makes it impossible for join_view to do the right thing here.

Proposed change:

Resolve LWG3698.

[inbal2l]

Scheduled for SG9's meeting in Kona, third session (13:00-15:15): https://wiki.edg.com/bin/view/Wg21kona2022/SG9

[JeffGarland]

This was discussed in LWG (LEWG-SG9 Joint session minutes) on Tue in Kona -- agree this is an issue -- resolution will be worked.

[jensmaurer]

Remove the SG9 label; assigning to LWG.

[JeffGarland]

There is a paper coming that addresses the issue. Draft form is here: https://isocpp.org/files/papers/D2770R0.html also linked from https://cplusplus.github.io/LWG/issue3698