Rollup of 5 pull requests
Successful merges:
- #103087 (Documentation BTreeMap::append's behavior for already existing keys)
- #103089 (Mark derived StructuralEq as automatically derived.)
- #103102 (Clarify the possible return values of `len_utf16`)
- #103109 (PhantomData: inline a macro that is used only once)
- #103120 (rustdoc: Do not expect `doc(primitive)` modules to always exist)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
a501e6699e