* link: respect `is_external` prop and other attributes on A tag
Instead of passing all props to NextLink by default, only pass props that
NextLink understands, placing the remaining props on the Radix link
Add a test case to avoid regression of `is_external` behavior.
* Link is a MemoizationLeaf
Because Link is often rendered with NextLink as_child, and NextLink breaks if
the href is stateful outside of a Link, ensure that any stateful child of Link
gets memoized together.
