No functional changes. The outliner selection operators shared many different functions for selection, activation, mode toggling, and other actions, but the code paths were not always clear, making any changes difficult. This cleans up the code and uses outliner_item_select() as the base function for selection, activation, mode toggling between the different selection operators. It also prepares for future features and fixes. Reviewed By: Severin Differential Revision: https://developer.blender.org/D5817