Layers rearrangement improvements

[miina]

Feature Description

There a few bugs / missing features in the layers arrangement currently that should be implemented:

• Drag and drop for multiple layers: (select 2 layers and drag-drop them in the Layers Panel - doesn't work, you can only drag-drop groups or single layers).
• Same as above but via keyboard
• Keyboard rearrangement (of any kind) is not possible in the Layers Panel currently, the user first needs to select the layer on canvas. It should be possible to rearrange when entering the Layers Panel via keyboard
• It should be possible to rearrange groups using cmd+up and cmd+down

Alternatives Considered

Additional Context

See #11884 (comment) for original discussion

[miina]

Ping @merapi for prioritization