Bug 254062

Like SVGFilter, CSSFilter should always intersect the FilterEffect imageRect with its primitiveSubregion. This will require:

1. Filter::ClipOperation will be removed.
2. Filter::clipToMaxEffectRect() will always clip the rectangle with maxEffectRect.
3. FilterEffect::calculateImageRect() will return the maxEffectRect if number of input effects is zero. This was a bug which was covered by the union mode of Filter::clipToMaxEffectRect().
4. RenderLayerFilters::beginFilterEffect() should set its targetBoundingBox the sourceImageRect of FilterTargetSwitcher.
5. SVGFilterGraph::getNamedNodes() should not return an error if one of the inputs is builtin and there is no node for it. This happens when we build a graph of primitives and one of the inputs is SourceGraphic or SourceAlpha. In this case we just need to ignore this input since there is no built-in primitive for it. This fixes the calculation of the filter outsets which was covered by  the union mode of Filter::clipToMaxEffectRect().