Implement DnD reordering

[leolost2605]

Pretty much replicates the plank remove and reorder experience 1 : 1

[lenemter]

For some reason I can remove unpined apps by dragging into nothing.

[lenemter]

And I think the Launcher object being a drop target is wrong, we need to insert a separate drop target object in between the launchers and expand them on hover, like the Plank does.

[leolost2605]

Unpinned apps can't be removed anymore.
Also I added animations when reordering and the poof animation. The reordering and removing experience should therefore be almost the same as with plank now.
Currently there is a bug in GTK4 < 4.8 that CSS animations sometimes just don't play that is noticeable when reordering but that's fixed with this PR and I tested it with 4.10 and it works really good there. I'm not very experienced with CSS so it's a very basic animation but IMO it looks pretty similar to the plank one. Still if somebody has ideas to improve it they're very welcome.
Admittedly the poof animation seems like a bit of a hacky solution but it works and I had only the plank svg to work with 🤷. Also the poof animation now is the same size as the icons whereas in plank it was a bit bigger, I'm not sure which way to go here?

[leolost2605]

Hmm just removing an app nothing else?

[lenemter]

@leolost2605 yep

[leolost2605]

@lenemter that is strange, cause I don't get these glitches...
I'm not very familiar with how gtk draws stuff but is it possible that different gala or gtk versions do something like that?
Also do you get the poof animation?

[lenemter]

I'm not very familiar with how gtk draws stuff but is it possible that different gala or gtk versions do something like that?

TBH I'm not familiar with this either. I remember seeing similar glitches in Sideload app and the cause was that window didn't smoothly change its size. It was easy to fix thanks to Gtk.Stack.interpolate_size, but since here's no stack used, I don't know if that can be the source of issues.

Also do you get the poof animation?

Oh yes, I do. It's a bit small though.

[leolost2605]

I no longer encounter glitches, but I can resize the dock now :)

Ok the last commit adds decorated=false which fixes all glitches for me and keeps the resizable=false. I hope that might also fix yours?

[lenemter]

Sorry it took so long to review. I left inline comments on things I personally don't like

[lenemter]

I tried this branch in Wayland session and it's totally broken, you can't remove an app using dragging, and when dragging there is no icon at all. This is definitely some Wayland issues, so worth asking @tintou

[danirabbit]

@lenemter Would you be okay with merging for now since it's working in X and then we can keep iterating since we're such early days here? It would be nice to keep momentum going to replace plank ASAP imo

[danirabbit]

@leolost2605 can you resolve conflicts here please? :)

[leolost2605]

@danirabbit done!

[lenemter]

This is something we have to revisit later but it's good enough to start testing the dock. Thanks for working on this <3