The text cursor follows slightly different "intuitive" rules than the
regular hit testing. Clicking past the right edge of a text box should
still "hit" the text box, and place the cursor at its end, for example.
We solve this by adding a HitTestType enum that is passed to hit_test()
and determines whether past-the-edge candidates are considered.
This works everywhere right now, but it's obviously not going to stay
that way forever. :^)
Note that this does not advance the cursor correctly for whitespace
since the cursor is DOM-based and doesn't take whitespace collapsing
into account yet.
Each Web::Frame now has a cursor that sits at a DOM::Position. It will
blink and look like a nice regular text cursor.
It doesn't really do anything yet, but it will eventually.
