Rework AdaptiveLayoutView

[joulei]

This PR introduces significant changes to our adaptive layout system, moving away from the previous DSL-heavy approach to a more flexible solution. It also introduces a new CachedWidget to optimize widget reuse across UI updates.

Key Changes

1. Reworked AdaptiveViewLayout into AdaptiveView:

   • Simplified DSL usage
   • Introduced a variant selector mechanism for dynamic layout selection
   • Instead of having a single widget instance (of the widget to be adapted), we use separate DSL groups for each variant. This allows for a lot more flexibility when it comes to UI tree manipulation. However this implies having different widget instances by default for the different variants. This is important when considering live-resizing the application, where widgets will be reinitialized and their state management must be prepared for it. We plan on supporting state serialization which will take care of porting state between the widget instances without much manual intervention. For now, we're using CachedWidget to avoid re-initializing and porting state between instances.
   • Updated all existing usages of AdaptiveViewLayout to use the new AdaptiveView

2. Introduced CachedWidget:

   • Allows reuse of complex widget instances across UI updates (wraps a widget in a singleton)
   • Particularly useful for maintaining state during live resizing
   • Implemented for RoomScreen and RoomsList to preserve their state

3. Improved flexibility

   • AdaptiveView now uses a closure-based selector for determining layouts. This allows to define AdaptiveViews that for example adapt to their parent size instead of just the screen size.
   • Direct access to Cx provided in variant selectors for more control

Limitations and Future Work

• Some limitations exist in the current implementation, particularly around widget finding and caching
• Both AdaptiveView and CachedWidget will be ported to Makepad core soon, addressing current limitations
• Detailed documentation and known limitations are provided in the code comments

Please refer to the inline documentation in adaptive_view.rs and cached_widget.rs for usage instructions and current limitations.

[kevinaboos]

Phenomenal work, thanks! All looks good.