Make sure the button still has the .image-button style class with an icon,
also add it to the initial state with only an arrow. Add a new
.arrow-button style class for the icon+arrow state so it's possible to
style it.
Remove spacing from the label+arrow variant to match, re-add it from the
stylesheet for both.
Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/3501
Not for symbolic icons.
Don't apply `-gtk-icon-filter: opacity(0.5);` to the symbolic icons as
they already have the "gray" colors indicating the disabled state.
Symbolic icons can be styled using the `color` property.
Also remove the obsolete comment.
The use of the keyboard-activating CSS class for buttons was added
in [1], but the style did not apply to buttons with has-frame=FALSE.
[1] 00923615f4 ("button: Add back visual feedback for keynav", 2021-04-01)
Rename the included theme to Default, with 4 variants:
light, dark, hc, hc-dark. This replaces Adwaita,
Adwaita:dark, HighContrast and HighContrastInverse.
We still make the themes available under these names,
and we still set up Adwaita-dark and HighContrastInverse
as the dark variants of Adwaita and HighContrast.
The unification of the theme variants under Default
is not quite perfect; it would be nice to merge
the assets/ and assets-hc/ subdirectories and render
all assets from a single svg file.
