Performance Improvement

- Because querying the Bounds property of an ISvgBoundable or
  SvgVisualElement is expensive, we introduced an ImmutableBoundable that
  is used by the SvgRenderer. This class stores the bounds of the supplied
  ISvgBoundable so that multiple queries for the bounds do not hamper
  performance when rendering.

- Converted the Bounds property on ISvgBoundable and SvgVisualElement to a
  CalculateBounds method to indicate that it is an expensive operation
  that returns a new value each time it is called.

- Removed redundant ISvgBoundable Location and Size properties.

- Fixed a bug in SvgFragment.Path property by converting it to a method that
  indicates it returns a new GraphicsPath instance when called and by
  disposing of that instance in CalculateBounds. There are many more
  instances of GraphicsPath not being disposed in the code base but we did
  not address that here.