Dropping/coalescing smallest should perhaps work on outer rings, not features

With complex MultiPolygon features, it would probably be useful if dropping/coalescing the smallest features as needed would also work on outer rings rather than only on whole features.

Likewise with densest, but it is more complicated to do because the rings are not already in quadkey order. (But perhaps they could be?)

The issue names no files, tests, or entry points. Start by locating the C++ code handling dropping/coalescing smallest features and densest ordering, then compare behavior for whole features and outer rings. Done means the requested outer-ring behavior is defined and validated for both cases, or the limitation is documented.

Written by the indexing model from the issue text.