fix: detect delete areas using pointer coordinates

[mikeharv]

The basics

• I validated my changes

The details

Resolves

Fixes #10077

Proposed Changes

• Dragger: Delete-area detection during pointer drags now uses the cursor position (PointerEvent.clientX / clientY) instead of the block’s workspace origin (getRelativeToSurfaceXY()). Block movement is unchanged; only hit testing for delete styling, drag-target hooks, and drop/delete on onDragEnd follow the pointer.
• WorkspaceSvg.getDragTarget: Accepts only PointerEvent once again.
• Keyboard drags: onDrag skips delete-area logic when the event is not a PointerEvent; onDragEnd commits without delete-area checks.

This effectively reverts one particular change introduced by #9593

Reason for Changes

Previously, deletion could trigger when the block origin overlapped a delete area even if the cursor was elsewhere, for example, dragging a block over the workspace while its top-left corner still intersected the toolbox column. Now, deletion depends on where the user is pointing, not where the block’s origin happens to be.

This conveniently seems to resolve #10076 as well, likely due to getRelativeToWorkspaceXY() returning the wrong sort of coordinates for zoomed workspaces. (I did not bother to root cause this, but did confirm it's no longer happening.)

Test Coverage

New mocha suite simulating realistic drags with delete areas.

• Drag to trashcan center - delete styling applied; block disposed on drop.
• Drag to toolbox center - same behavior for toolbox delete area.
• Origin overlaps toolbox, cursor outside - block origin moved slightly into toolbox delete rect; cursor stays outside; no delete styling; block survives onDragEnd.