Add tests for SVG 2

[PolariTOON]

This PR adds tests for properties defined in SVG 2.

For a better reviewability, this PR is split into several commits : one for each section of the spec.

The following properties only appear in the Candidate Recommendation:

• text-decoration-fill
• text-decoration-stroke
• color-rendering

The following properties only appear in Editor's draft:

• stop-color
• stop-opacity

[Zefling]

Thank you.