Rollup merge of #142058 - xizheyin:rustc-attr-parsing, r=jdonszelmann

Clean `rustc_attr_parsing/src/lib.rs` documentation

Improves the documentation clarity in `rustc_attr_parsing` by restructuring content with clearer section headers, simplifying explanations of attribute types, making technical descriptions more precise.

r? ``@oli-obk``

Author: matthiaskrgr