Avoiding the very high constrast pure black results in cartographically
more pleasing styles, so it's nice to do this by default.
This should result in nicer looking maps being created in QGIS
when users don't do any manual style tweaks.
Using this renderer no symbol will be drawn for features, but labeling,
diagrams and other non-symbol parts will still be shown.
Selections can still be made on the layer in the canvas and selected
features will be rendered with a default symbol. Features being edited
will also be shown.
This is intended as a handy shortcut for layers which you only want
to show labels or diagrams for, and avoids the need to render
symbols with totally transparent fill/border to achieve this.
(fix#12131)