Since Core::Object properties are really only used by GML now that the
Inspector is long gone, there's no need for these to pollute
Core::Object.
This patch adds a new GUI::Object class to hold properties, and makes
it the new base class of GUI::Window, GUI::Widget and GUI::Layout.
The "instantiate an object by name" mechanism that GML uses is also
hoisted into GUI::Object as well.
The existing `load_from_gml()` methods look the same as before from the
outside. Inside though, they now forward to `try_load_from_gml()` which
returns Error when things go wrong. It also now calls the `try_create()`
factory method for Objects instead of the `construct()` one.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
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.
