Restrict "sort items" assist for traits & impls
This restricts the "sort items alphabetically" assist when the selection is inside a `Impl` or `Trait` node & intersects with one of the associated items.
It re-orders the conditional checks of AST nodes in the `sort_items` function to check for more specific nodes first before checking `Trait` or `Impl` nodes. The `AssistContext` is passed into the `add_sort_methods_assist` function to check if the selection intersects with any inner items, e.g. associated const or type alias, function. In this case the assist does not apply.
Fixes: #14516
5111207d9a