Fix fullscreen fill-extrusion querying at low pitch

[arindam1993]

The way query geometry was being constructed for fill-extrusions was incorrect for bounds based queries in which the point underneath the camera would fall within the query volume.

This PR fixes it by considering all 4 possible cases

1. The point underneath the camera is not behind the query bounds, in this case ignore it
2. The point is exactly behind, in this case insert it between the last two points
3. The point is behind and to the left, so replace the 4th point
4. The point is behind and to the right, so replace the 3rd point.

I've added some ASCII art code comments to make it clearer.

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• tagged @mapbox/gl-native if this PR includes shader changes or needs a native port
• apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'
• add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog>Fill fullscreen fill-extrusion querying at low pitch.</changelog>

[ansis]

Looks good to me!

The way bufferedCameraGeometry depends on the order of the polygonizeBounds return value seemed a bit fragile to me at first but I can't think of a better approach. And the polygonizeBounds documentation is very explicit about the order.

One small nit.

[ansis]

Would cameraPolygon.splice(3, 0, this.cameraPoint) work here?

[arindam1993]

yes derp, I keep forgetting splice can be usedlike that