fix order of 3D features in query results (fix #7883)

[ansis]

This fixes #7883, a bug where a query returned 3D features after 2D features even if they were rendered above them. Query results should be returned in the order the features are rendered.

The fix is somewhat tricky because the order of features can get complicated:

• The order between features in two 2D layers is always determined by layer order
• The order between features in two 3D layers is always determined by depth.
• The order between a 2D and 3D feature can depend on a 3rd layer if the 3rd layer contains a 3D feature that is closer than the other 3D feature.

This sorts features in the order they are rendered and adds a query test to make sure that is the case.

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• manually test the debug page