[libc++][ranges] P3060R3: Add `std::views::indices(n)` (#146823)
Implements [P3060R3](https://wg21.link/P3060R3)
Closes #148175
# References
- https://github.com/cplusplus/draft/issues/7966
- https://github.com/cplusplus/draft/pull/8006
- https://wg21.link/customization.point.object
- https://wg21.link/range.iota.overview
- https://wg21.link/ranges.syn
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Co-authored-by: Hristo Hristov <zingam@outlook.com>
Co-authored-by: A. Jiang <de34@live.cn>