Operator combines more features and it wasn't very transparent which properties are used in which feature and how they are used. Features linked_time, side_of_frame and linked_handle are isolated, logic moved into own function. deselect_all property was removed as it practically equals to !extend in all cases. Functional change: Dragging existing selection will not change active strip. Previously this could happen if click happened on strip that wasn't active. Reviewed By: campbellbarton Differential Revision: https://developer.blender.org/D12320