Update Linux/XDG default theme selection

[lucor]

Description:

This commit update the Linux/XDG default theme selection as per https://github.com/flatpak/xdg-desktop-portal/blob/1.16.0/data/org.freedesktop.impl.portal.Settings.xml#L32-L46

Relates to: #2657 #3414

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

Coverage: 61.768% (-0.06%) from 61.824% when pulling 9bcee24 on lucor:xdg-default-theme-selection into fe77710 on fyne-io:develop.

[Jacalz]

It seems to me that the previous behavior was doing the right thing (or Gnome is not following the protocol correctly) because this change makes the switch between dark/light not work anymore for me.

I would suggest that we use light theme for both 0 and 2 instead.

[andydotxyz]

But previously dark was our default if nothing was specified outside of this lookup...

[Jacalz]

But previously dark was our default if nothing was specified outside of this lookup...

Yes, but what's the point of having this theme switching support if it isn't possible to switch between light and dark? With this change, the application is always dark no matter what you do.

We have already passed the stage where we know that the desktop supports the protocol so those that do not will still default to dark.

[andydotxyz]

Thanks for getting a good solution to this one

[andydotxyz]

Thanks