Auto merge of rust-lang#107191 - Voultapher:reverse-timsort-scan-direction, r=thomcc

Reverse Timsort scan direction

Another PR in the series of stable sort improvements. Best reviewed by looking at the individual commits.

The main perf gain here is for fully ascending (sorted) or reversed inputs for cheap to compare types such as `u64`, these see a ~1.5x speedup.

![timsort_evo2_hot_u64_10k](https://user-images.githubusercontent.com/6864584/213913351-cfdf452f-a37c-4bc6-a811-d10c60e66eca.png)

![timsort_evo2_hot_string_10k](https://user-images.githubusercontent.com/6864584/213913354-d9cc395a-2b48-4f54-b687-09174b9e35ce.png)

Types such as string with indirect pre-fetching see only minor changes. Further speedups are planned in future PRs so, I wouldn't spend too much time for benchmarks here.

Author: bors