Attach a 'job' to the main thread event loop, trusting that the event
loop implementation will cancel it when asked to quit. This is something
that our Unix implementation does, but isn't strictly part of the
contract of EventLoopImplementation.
With this change we save a copy of of scroll state at the time of
recording a display list, instead of actual ScrollState pointer that
could be modifed by the main thread while display list is beings
rasterized on the rendering thread, which leads to a frame painted with
inconsistent scroll state.
Fixes https://github.com/LadybirdBrowser/ladybird/issues/4288
Skia has a check in debug mode to verify that surface is only used
within one thread. Before this change we were violating this by
allocating surfaces on the main thread while using and destructing them
on the rendering thread.
The display list is an immutable data structure, so once it's created,
rasterization can be moved to a separate thread. This allows more room
for performing other tasks between processing HTML rendering tasks.
This change makes PaintingSurface, ImmutableBitmap, and GlyphRun atomic
ref-counted, as they are shared between the main and rendering threads
by being included in the display list.
