Tests that recursive 'use' instances do not block rendering.

Various scenarios that directly and indirectly create circular references via the 'use' tag. A 'g' element is used when structural elements are necessary. None of the 'use' scenarios render anything. 'useLongCycle' tests a chain of recursive 'use' instances that eventually cycles back to the first element. In 'useNested' 'use' elements are nested, with the child referring to the parent. In 'useNestedGroup' a 'use' instance references a parent 'g' element. In 'useIndirectNestedGroup' a 'use' instance indirectly references its own parent 'g'. In 'useMultipleIndirectNestedGroup', two 'use' instances reference their parent 'g' elements, and additional 'use' instances refer to these self-referencing 'use' elements. A green 'rect' is used to verify that rendering was processed up to that point.