The `get` half of this machinery was already implemented, but the `tuple_size`
and `tuple_element` parts were hiding in [ranges.syn] and therefore missed.
Differential Revision: https://reviews.llvm.org/D108054
We've been forgetting to add those to most of the <ranges> review.
To avoid forgetting in the future, I added an item in the pre-commit
checklist.
Differential Revision: https://reviews.llvm.org/D106287
A few slipped through the cracks because D104175 and D104170 didn't
concern themselves with newer commits.
Differential Revision: https://reviews.llvm.org/D104414