Rollup merge of #154664 - okaneco:integer_cast_extras, r=scottmcm

core/num: Implement feature `integer_cast_extras`

Tracking issue rust-lang/rust#154650
Accepted ACP rust-lang/libs-team#765 (comment)

Implement `saturating`, `checked`, and `strict` casting between signed and unsigned integer primitives of the same bit-width.

Add `cast_integer` panic function to `overflow_panic.rs`

Author: JonathanBrouwer