NOTE: This change shouldn't have any visible effect. It's just the first (easiest) step towards decoupling gizmo redraws from viewport redraws. We currently redraw the entire region whenever a gizmo needs redrawing, which would be nice to avoid in the future, see T73198. The first step towards this would be having a separate tag for them, which is what this patch implements. The term "editor-overlays" was chosen because for the forseeable future, we'll also have to redraw non-gizmo overlays in-between drawing 3D and 2D gizmos. Namely annotations. Reviewed By: brecht Differential Revision: https://developer.blender.org/D6838