* [FEATURE] Selective masking
Advanced rendering feature that allows the definition of 'masks' areas around labels or with a new typ of symbol layer. These masks will "un-draw" symbol layers of other layers underneath.
It modifies the rendering process by adding an optional second pass.
that these are automatically respected whenever the format is
rendered using QgsTextRenderer
This is done transparently to the caller - so by porting away
from the raw QPainter text apis to use QgsTextRenderer instead,
then they immediately gain the ability to use data defined
properties in their text formats.
Allows for rendering a marker symbol in the background of labels
(complementing the existing shapes/SVG choices). This allows use
of QGIS marker symbology as a background symbol behind labels (e.g.
for highway shield labels)
The new QgsRenderContext::TextRenderFormat enum controls how text
should be handled during a render operation, e.g. whether to render
text as outlines (paths) or keep it as real text objects.
Deprecate previous arguments in QgsTextRenderer which handled
this same use case.
This allows us to make the setting vary per-render, instead of
having a single global flag controlling the setting. Ultimately
this will allow us to have different behaviour within the
canvas renders vs print layout exports.
Refs #3975
