Outliner: Object state filter invert toggle

This adds an invert toggle for the outliner object state filters.
There are some cases where we want a filter for invertable states (Selected,
Unselected) and having a single toggle to invert the filter reduces the
number of separate filter types needed. This removes the "Hidden" filter
which can now be replicated with an inverted "Visible" filter.

Differential Revision: https://developer.blender.org/D9598

release/scripts/startup/bl_ui/space_outliner.py

@@ -372,10 +372,16 @@ class OUTLINER_PT_filter(Panel):
         row = col.row()
         row.label(icon='OUTLINER_COLLECTION')
         row.prop(space, "use_filter_collection", text="Collections")
+
         row = col.row()
         row.label(icon='OBJECT_DATAMODE')
         row.prop(space, "use_filter_object", text="Objects")
+        row = col.row(align=True)
+        row.label(icon="BLANK1")
         row.prop(space, "filter_state", text="")
+        sub = row.row(align=True)
+        sub.enabled = space.filter_state != 'ALL'
+        sub.prop(space, "filter_invert", text="", icon="ARROW_LEFTRIGHT")
 
         sub = col.column(align=True)
         sub.active = space.use_filter_object