Rollup merge of #118811 - EbbDrop:is-sorted-by-bool, r=Mark-Simulacrum

Use `bool` instead of `PartiolOrd` as return value of the comparison closure in `{slice,Iteraotr}::is_sorted_by`

Changes the function signature of the closure given to `{slice,Iteraotr}::is_sorted_by` to return a `bool` instead of a `PartiolOrd` as suggested by the libs-api team here: rust-lang/rust#53485 (comment).

This means these functions now return true if the closure returns true for all the pairs of values.

Author: Nadrieril