Add indexable vector layer cache
Major redesign of attribute table, codename: dual view
Add tests for attribute table / dual view
Fix issue #7169
If removing multiple attributes, remove the indices in descending order, so it does not get confused
Remove unneeded variable
Add tests for QgsVectorLayerCache
Fix: emit committedFeaturesAdded and committedFeaturesRemoved
Fix: Check for existence of data provider to prevent segfault