Rollup merge of rust-lang#107935 - petrochenkov:attreorder, r=michaelwoerister

rustc_ast: Merge impls and reorder methods for attributes and meta items

Merge `impl` blocks for the same types, change order of methods to be more predictable and consistent between impls.
No functional changes.
Follow up to rust-lang#107569.

Author: matthiaskrgr