Rollup merge of #128376 - compiler-errors:finish-ur-vegetables, r=jieyouxu

Mark `Parser::eat`/`check` methods as `#[must_use]`

These methods return a `bool`, but we probably should either use these values or explicitly throw them away (e.g. when we just want to unconditionally eat a token if it exists).

I changed a few places from `eat` to `expect`, but otherwise I tried to leave a comment explaining why the `eat` was okay.

This also adds a test for the `pattern_type!` macro, which used to silently accept a missing `is` token.

Author: matthiaskrgr