Rollup merge of #136690 - Voultapher:use-more-explicit-and-reliable-ptr-select, r=thomcc

Use more explicit and reliable ptr select in sort impls

Using `if ...` with the intent to avoid branches can be surprising to readers and carries the risk of turning into jumps/branches generated by some future compiler version, breaking crucial optimizations.

This commit replaces their usage with the explicit and IR annotated `bool::select_unpredictable`.

Author: matthiaskrgr