add option to return MODIFIED rows rather than 3 types of modified

Not everyone wants to distinguish between geom and attrib changes.
I'd consider making this the default, ADDITIONS/DELETIONS/MODIFICATIONS seems like a more standard pattern.

Start by locating the code that classifies and returns changed geodata rows, then inspect how geometry and attribute changes are currently represented. Define the option's behavior and default consistently, and verify that callers can receive a single MODIFIED category instead of the three existing modified types.

Written by the indexing model from the issue text.