Runs the cell of the tiling pattern a colour selected, reporting its events to processor, in the middle of
the current event: call it from a processor callback, as often as the processor needs (once per pattern and scale, say).
public bool RunPatternCell(in PdfColor color, ContentProcessor processor)
The pattern colour, such as FillColor in PaintPath(in PathEvent, ContentContext).
The processor that receives the cell's events (this run's or another).
true when the cell ran; false when the colour does not select a valid tiling pattern, or
the cell would run inside itself (recorded as ContentPatternRecursion) or deeper than
MaxNestingDepth (ContentNestingTooDeep).
ISO 32000-2 §8.7.3.1, steps a to d: the cell runs between an implicit save and restore (SaveState(ContentContext) and RestoreState(ContentContext)), from the graphics state at the beginning of the stream that selected the pattern (its blend mode, alpha constants and soft mask at their defaults, §11.6.7), with the CTM set to the pattern space (GetPatternSpace(in PdfColor)), the clip intersected with the cell's bounding box (a Rectangle clip event), RunKind Pattern and the pattern's resources (the current ones when it has none). One cell is run, at the origin of pattern space; replicating it every XStep and YStep is the processor's.
§8.7.3.3: for an uncoloured pattern the current colours are the colour given with the pattern, in the underlying colour space,
and colour operators, sh and anything run from the cell that sets colours are ignored with a diagnostic.