refactor!: port preferences to libadwaita

[garaevdi]

Tried to keep it as faithful to the original as possible, but there are still some notes:

• Setting custom corners radius and smoothing isn't working, though for me even on main branch it isn't working
• When entering EditShadowPage GTK complaining about something related to focus, but it works and so be it
• I'm not quite fun of how PaddingsRow turned out, but I couldn't come up with something better. If you have any suggestion, I'd be happy to implement them
• I dropped gnome-shell 45, since ResetPage uses Adw.AlertDialog which was introduced in 1.5, but gnome-shell 45 usually comes only with 1.4. If this a no-no move, I can change it to Adw.MessageDialog
• I didn't include any .po files in this PR, since I don't know how to properly handle them

[flexagoon]

This looks awesome, thanks!

A few issues though:

1. This looks pretty weird on small window sizes. You should probably add a padding between the button and the text here and on the "custom" page.

2. There is a noticeable lag when entering the custom shadow page

[flexagoon]

The linter errors are due to formatting. You should run npx biome format --write src/ on your code and also use the "Organize imports" LSP action.

[garaevdi]

@garaevdi LGTM. There is still lag when opening the shadow edit page though. Do you know what this may be related to?

I think this is mostly due to loading of the background picture. I thought about alternate ways to implement this, like use GdkPixbuf and maybe load image asynchronously, but this would be either as slow as it already is, there would be some kind of loading before the page is shown or the picture would pop afterwards.

The ultimate solution would be a complete removal of background image, but IMHO then this page will lose half of it's charm.

[flexagoon]

Thanks a lot for the contribution!