* drop `@ts-expect-error`, because `inert` is available now
* fix logical error
We want to apply `inert` when we _don't_ have nested dialogs, because if
we _do_ have nested dialogs, then the inert should be applied from the
nested dialog (or visually the top most dialog).
* update changelog
* replace `useInertOthers` with `useInert`
* add `assertInert` and `assertNotInert` accessibility assertion helpers
* ensure the `main tree` root is marked as inert
As well as the parent dialogs in case of nested dialogs.
Robin Malfait