Rollup merge of #95566 - eduardosm:std_char_consts_and_methods, r=Mark-Simulacrum

Rollup merge of #95566 - eduardosm:std_char_consts_and_methods, r=Mark-Simulacrum

Avoid duplication of doc comments in `std::char` constants and functions

For those consts and functions, only the summary is kept and a reference to the `char` associated const/method is included.

Additionaly, re-exported functions have been converted to function definitions that call the previously re-exported function. This makes it easier to add a deprecated attribute to these functions in the future.