`<mdspan>`: Cleanup `extents`'s deduction guide#3632

Merged

StephanTLavavej merged 2 commits intomicrosoft:feature/mdspan2from

JMazurkiewicz:mdspan/extents-deduction-guide

Apr 7, 2023

Commits on Apr 4, 2023

Fix `extents` deduction guide
JMazurkiewicz
committed

Commits on Apr 6, 2023

Drive-by: alias repeating `layout_right::mapping`
JMazurkiewicz
committed