Emit event when NcAppContent list pane is resized

[julien-nc]

The upper context sometimes needs to know when the list pane is resized. If, for example, the content of the NcAppContent's default slot needs to be re-rendered or needs to adjust its layout/size.

Concrete use case: GpxPod displays a Maplibre map that:

• reacts if the window is resized 🎉
• does not react if its container size changes 😞 We need to explicitly tell the map component to resize when this happens.

Suggestion: Emit resize:list in NcAppContent when Splitpanes (the 'list' slot) is resized by the user.
What do you think?