Rather than disable and re-enable the timer, always keep it active
and make it do collision checks to decide if it should have an effect.
This is because set_automatic_scrolling_active(true) calls the
timeout callback immediately before starting the timer, and
when clicking the gutter this callback could disable the timer
again (if the first page scroll put the scrubber under the cursor).
Intead of making set_automatic_scrolling_active() work when it's
called reentrantly (which is easy: just swap the order of
on_automatic_scrolling_timer_fired() and timer->start() so that
on_automatic_scrolling_timer_fired() can immediately stop the
timer again, but it's confusing), make the timer check if it
should do anything.
This is keyed off m_last_mouse_position instead of
m_hovered_component because m_hovered_component is a visual state
and we arguably shouldn't modify it while the left mouse button
is down (as it indicated what part is activated on click).
Most callers of set_automatic_scrolling_active() also change
m_automatic_scrolling_kind, and it makes it possible to make timer
behavior dependent on the autoscroll kind later.
It's slightly less code, and m_scrubber_in_use is now set correctly
when shift-clicking, keeping the mouse button down, and then
dragging the throbber.
The shift-click brings the scrubber under the cursor, and then
the scrubber_rect().contains() condition is true and both scrubber
drags and shift-click-drags are handled the same naturally.
In order to calculate a thumb size that is a representation
of the visible portion (page) of the content, that information
needs to be taken into account.
You can now #include <AK/Forward.h> to get most of the AK types as
forward declarations.
Header dependency explosion is one of the main contributors to compile
times at the moment, so this is a step towards smaller include graphs.
