cluster geometry is offset from original overlapping points

Nobody has claimed this yet.

**mapbox-gl-js version**: 1.6.1

**browser**: any, but using latest Chrome

### Steps to Trigger Behavior

1.create a cluster from a source that has 2 overlapping features
2.click on the cluster, report the feature geometry from the click handler
3.note that the cluster feature's geometry in the click event handler is off from the original geometry

This was discussed previously on: https://stackoverflow.com/questions/59667369/cluster-geometry-differs-from-original-geometry-has-an-offset-but-why

The issue is not in supercluster, there the cluster is calculated correctly.

### Link to Demonstration
https://jsfiddle.net/bartvde/t9vm12qf/16/

### Expected Behavior
The geometry in the click handler is the same as the original 2 overlapping feature's geometry

### Actual Behavior
The geometry reported in the click handler is offset

Start with the linked JSFiddle and its click handler, reproducing the case with two overlapping features and comparing the reported cluster geometry with the original geometry. Trace where the cluster feature geometry is produced for click events. Done means the handler reports the original geometry without an offset.

Written by the indexing model from the issue text.