resolveHrefChain

Resolves the referenced gradient's attributes and stops, producing a copy of THIS gradient's type with merged attributes and the correct stop children.

Per SVG spec:

• Local attributes override referenced gradient's attributes.

• If the referencing gradient has its own stops, they are used. Otherwise, the referenced gradient's stops are inherited (following the href chain if needed).

• The element type of the referencing gradient determines the brush type, even when the referenced gradient is a different type (cross-type href).