Merge topic 'speedup-opengl-plotpoints'

77aff9ba vtkScatterPlotMatrix: persist plots across animation frames
e476ed59 ScatterPlotMatrix: Use enums for animation phase
582a388d Context2D: context items can release graphics cache objects
4d91ce8d Speed up rendering of selected points in 2D, 3D plots
47222e03 Refactor common method to filter selected points in vtkPlot
55993cd8 Plot2D: Speed up 2D point rendering
1a37ea5b Plot3D: Speed up 3D point rendering
21b5a3aa Context2D: abstract cached-draw API.
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Reviewed-by: Sankhesh Jhaveri <sankhesh.jhaveri@kitware.com>
Merge-request: !10262