This abstracts out a common helper to determine focusable area kind
which is used by `Element::is_click_focusable`,
`Element::is_sequentially_focusable`, and `Element::is_focusable_area`.
This avoid having the latter depend on the former two, which was the
reverse of what the specification said. The helper is necessary because
the specification defines click and sequential focusability as subsets
of focusable elements, but going from "This is a focusable element" to
determining what kind of focusable element something is requires
duplicating a lot of the logic that was used to determine that something
is a focusable area.
It's likely that the specification needs more work here to improve the
definition (and indeed to unify all of the places that talk about what
elements are focusable areas). For now, this just tries to make our code
more similar to the text.
See: whatwg/html#4607
Testing: This shouldn't change behavior, so should be tested by existing
tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
e2f6852a45