Rollup merge of rust-lang#121277 - reitermarkus:generic-nonzero-convert-num, r=dtolnay

Refactor trait implementations in `core::convert::num`.

Tracking issue: rust-lang#120257

Implement conversion traits using generic `NonZero` type, and refactor all macros to use a consistent format/order of parameters.

r? `@dtolnay`

Author: matthiaskrgr