on mobile after dragging feature, can't pan map

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**mapbox-gl-js version**: ?
**mapbox-gl-draw version**: master

### Steps to Trigger Behavior

1. On mobile, drag a polygon and deselect it to make it blue.
2. Tap it once to make it orange with node handles. (if you double tap to get midpoint handles, the bug doesn't appear)
3. Drag the center of the polygon around and it moves. (if you don't do this step, the bug doesn't appear)
4. Drag somewhere outside the polygon to try to pan the map.

### Expected Behavior

I'd expect the map to pan without moving the polygon.

### Actual Behavior

The map doesn't pan, instead the polygon is moved to where you tried to pan.

Start by reproducing the mobile sequence in the issue: select and drag a polygon, then drag outside it to pan the map. Trace the map-drag and polygon-drag interaction entry points, and verify the fix by confirming that the map pans without moving the polygon after the stated steps.

Written by the indexing model from the issue text.