Platform preferences changes are not properly registered on Linux

[Christopher Schnick]

Hello,

it seems like the Platform preferences API does not properly register 
theme updates anymore in the latest desktop environments.

In my testing, it didn't work on Gnome 47.4 and KDE Plasma 6.3.2. The 
color scheme is always light and no updates are registered. The accent 
color is also always the default one.

On Gnome 46.0, when you change the dark mode setting, the GTK.theme_name 
is actually updated but the bgcolor and fgcolor properties are not, 
leading to the color scheme not being updated. But here, the properties 
are definitely detected correctly on initialization, it's just the 
updates that are not happening at runtime when something is changed.

Best
Christopher Schnick