Turn Linters', etc. implicit into_iter()s into explicit rules() (#5436)

## Summary

As discussed on ~IRC~ Discord, this will make it easier for e.g. the
docs generation stuff to get all rules for a linter (using
`all_rules()`) instead of just non-nursery ones, and it also makes it
more Explicit Is Better Than Implicit to iterate over linter rules.

Grepping for `Item = Rule` reveals some remaining implicit
`IntoIterator`s that I didn't feel were necessarily in scope for this
(and honestly, iterating over a `RuleSet` makes sense).

crates/ruff_dev/src/generate_rules_table.rs

@@ -102,10 +102,10 @@ pub(crate) fn generate() -> String {
                 ));
                 table_out.push('\n');
                 table_out.push('\n');
-                generate_table(&mut table_out, prefix, &linter);
+                generate_table(&mut table_out, prefix.clone().rules(), &linter);
             }
         } else {
-            generate_table(&mut table_out, &linter, &linter);
+            generate_table(&mut table_out, linter.rules(), &linter);
         }
     }