Rollup merge of #73694 - poliorcetics:self-upper-keyword, r=Mark-Simulacrum
Rollup merge of #73694 - poliorcetics:self-upper-keyword, r=Mark-Simulacrum

Document the Self keyword

Partial fix of #34601.

Document the `Self` keyword.

This contains simple examples of the places where `Self` can be used.

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust