xwidget events

[Po Lu]

I've been experimenting with making xwidget-webkit on X11 usable as an
actual web browser.  So far I've figured out the annoying redraw issues
and the broken scroll optimization, but I'm still puzzling over event
handling.

I was able to borrow a Mac from a friend today for an hour or so, and I
used it to try the NS xwidget implementation.  It seems to handle mouse,
button and click events entirely separately from the rest of Emacs,
which I don't think is a very good idea either.  But that also means the
browser is actually useful, which is a good thing.

In the existing X11 xwidget implementation, only some events, such as
motion events are passed through (without being exposed to Lisp code
first), while with the improvements to xwidget redisplay in bug#51473,
no events are passed through to the xwidget at all.

So I think a better idea would be the ability to pass through individual
input events via Lisp code (for instance with a function named
`xwidget-do-event', which would accept a lispy event as input and then
send an equivalent event to the xwidget).  Lisp code could then take
input events in the xwidget-webkit, and then send them to the xwidget.

But that's my take as a relative outsider to Emacs input, so someone
probably has a better idea.

Any thoughts?  Thanks.