Now that all input events are handled by LibWebView, replace the IPCs
which send the fields of Web::KeyEvent / Web::MouseEvent individually
with one IPC per event type (key or mouse).
We can also replace the ad-hoc queued input structure with a smaller
struct that simply holds the tranferred Web::KeyEvent / Web::MouseEvent.
In the future, we can also adapt Web::EventHandler to use these structs.
The Serenity chrome is the only chrome thus far that sends all input key
and mouse events to WebContent, including shortcut activations. This is
necessary for all chromes - we must give web pages a chance to intercept
input events before handling them ourselves.
To make this easier for other chromes, this patch moves Serenity's input
event handling to LibWebView. To do so, we add the Web::InputEvent type,
which models the event data we need within LibWeb. Chromes will then be
responsible for converting between this type and their native events.
This class lives in LibWeb (rather than LibWebView) because the plan is
to use it wholesale throughout the Page's event handler and across IPC.
Right now, we still send the individual fields of the event over IPC,
but it will be an easy refactor to send the event itself. We just can't
do this until all chromes have been ported to this event queueing.
Also note that we now only handle key input events back in the chrome.
WebContent handles all mouse events that it possibly can. If it was not
able to handle a mouse event, there's nothing for the chrome to do (i.e.
there is no clicking, scrolling, etc. the chrome is able to do if the
WebContent couldn't).
