This commit introduces a couple of connected changes that are hard to
untangle, unfortunately:
- Parse GML into the AST instead of JSON
- Change the load_from_json API on Widget to load_from_gml_ast
- Remove this same API from Core::Object as it isn't used outside of
LibGUI and was a workaround for the object registration detection;
by verifying the objects we're getting and casting we can remove this
constraint.
- Format GML by calling the formating APIs on the AST itself; remove
GMLFormatter.cpp as it's not needed anymore.
After this change, GML formatting already respects comments :^)
This widget provides a scrollable view onto another (child) widget.
If the child is larger than the parent, scrollbars are provided for
panning around the child.
