Support drag behavior for all selected components, not just blocks

[draedful]

Currently, the drag behavior in BlockController only affects selected blocks. When a user drags a block, it correctly drags all other selected blocks together, but it ignores other types of selected components (custom Layer components, groups, etc.) that might be selected through the SelectionManager.

Current Implementation

In BlockController.ts (lines 47-49):

graph/packages/graph/src/components/canvas/blocks/controllers/BlockController.ts

Lines 47 to 49 in 1cc4d99

	const draggingElements = block.context.graph.rootStore.blocksList.$selectedBlocks.value.map((block) =>
	block.getViewComponent()
	);

Expected Behavior

All selected components should participate in drag operations if they support dragging. The library should:

1. Distribute drag events to all selected components - When dragging, all selected components should receive DRAG_START, DRAG_UPDATE, and DRAG_END events
2. Support opt-in drag behavior - Components should have a draggable: boolean property to opt into drag support
3. Provide default drag implementation in GraphComponent - Basic drag logic (with snapping, autopanning, capturing, cursor support) should be available as default behavior in GraphComponent