Fixes for Polygons plotting with holes #3409
The PolygonPlot implementation switched between the MultiPolygons and Patches glyphs depending on whether the polygons have holes or not. The problem with that is that in a dynamic plot or HoloMap the returned data format may therefore change but the glyph is only initialized once, so a MultiPolygons glyph could end up with the data format for the Patches glyph and vice versa. This PR ensures that Polygons are always plotted using the MultiPolygons glyph unless a PolyDraw or PolyEdit stream is attached to the plot, which do not yet support holes. This ensures backwards compatibility while also fixing the bug.