[kbn-grid-layout][dashboard] Basic keyboard interaction (#208286)

## Summary
Adds keyboard navigation for drag-and-drop interactions
Fixes https://github.com/elastic/kibana/issues/211925
Fixes https://github.com/elastic/kibana/issues/190448

### Supported features 
1. Resize panels


https://github.com/user-attachments/assets/ba7add16-a0c6-4f15-9f3b-0f8ef7caf8ac

2. Drag panels within the same section (dragging between sections is
pending)


https://github.com/user-attachments/assets/a1fd80af-63ca-4fa2-bded-3db9968a8366

3. Move rows up/down


https://github.com/user-attachments/assets/8d7e8d7d-b1bf-4abe-9cc2-28eeea9b43f8

### Interaction Flow

1. Start interaction with `Space` or `Enter`
2. Move using arrow keys
3. Finish by confirming (`Enter`/`Space`) or canceling (`Escape`)
(blurring also confirms the changes)

### Scrolling Behavior:
* Default browser scrolling is disabled in interaction mode to avoid
unexpected behavior and edge cases that would overcomplicate this simple
implementation.
* Scrolling occurs when the user reaches the edge of the screen while
resizing or dragging, allowing them to continue the interaction
smoothly.
* When the operation is confirmed, we also scroll to the element to make
sure it's in view.

### Missing (planned for another PR):
* A11y announcements 
* Dragging between sections
* This feature is not well unit-tested, but it's very difficult to do it
without mocking the crucial pieces of functionality. I'd vote to leave
it for now and add a few functional tests once we decide a strategy for
it, since drag and drop interactions are anyway quite difficult to
unit-test reliably anyway.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

examples/grid_example/public/app.tsx

@@ -50,6 +50,7 @@ import { dashboardInputToGridLayout, gridLayoutToDashboardPanelMap } from './uti
 const DASHBOARD_MARGIN_SIZE = 8;
 const DASHBOARD_GRID_HEIGHT = 20;
 const DASHBOARD_GRID_COLUMN_COUNT = 48;
+const DASHBOARD_DRAG_TOP_OFFSET = 150;
 
 export const GridExample = ({
   coreStart,
@@ -67,6 +68,7 @@ export const GridExample = ({
     gutterSize: DASHBOARD_MARGIN_SIZE,
     rowHeight: DASHBOARD_GRID_HEIGHT,
     columnCount: DASHBOARD_GRID_COLUMN_COUNT,
+    keyboardDragTopLimit: DASHBOARD_DRAG_TOP_OFFSET,
   });
 
   const mockDashboardApi = useMockDashboardApi({ savedState: savedState.current });