Add displayId to DragPositioningCallback

Adds a `displayId` parameter to `DragPositioningCallback` methods
(`onDragPositioningStart`, `onDragPositioningMove`, `onDragPositioningEnd`).

This allows the callback to be aware of the display on which the drag
operation is occurring, which is necessary for multi-display window dragging.

Bug: 381172757
Test: run unit tests for related classes
Flag: EXEMPT no functional change
Change-Id: I3308968211c727e5c26d47d1335375e9bcbe0e86