Auto merge of #105671 - lukas-code:depreciate-char, r=scottmcm

Use associated items of `char` instead of freestanding items in `core::char`

The associated functions and constants on `char` have been stable since 1.52 and the freestanding items have soft-deprecated since 1.62 (rust-lang/rust#95566). This PR ~~marks them as "deprecated in future", similar to the integer and floating point modules (`core::{i32, f32}` etc)~~ replaces all uses of `core::char::*` with `char::*` to prepare for future deprecation of `core::char::*`.

Author: bors