[Renderer] Add support for connection Decorations

The support for Connection Decorations should be improved. This includes:

- Adding UML-specific CSS properties to identify the required semantic attributes (e.g. Directed Association, Composite Association...)
- Adding the missing decorations to the existing DecorationFactory
- Adding support for customization (Line attributes, e.g. Color, Width)
- Support decorations on the lines (e.g. GeneralOrdering)
- Support multiple/composite decorations (e.g. "Navigable composite owned by classifier") (Note: they must not be stacked on top of each other, but follow each other)
- Bonus step: Improve clipping of the Connection Line below the Decoration. Currently, zooming on an Arrow connection end doesn't show a perfect triangle, because the 1px-wide connection line below it looks like a rectangle when zoomed in:


Start by locating the renderer's existing Connection Decoration handling and the DecorationFactory mentioned in the issue. Review how UML semantic attributes and line customization are represented; done means the listed decorations, customization, line decorations, and ordered composite decorations are supported, with clipping improved if the bonus is included.

Written by the indexing model from the issue text.