`<clipPath>` support

[jwmcglynn]

• [x] Add support for parsing <clipPath> elements
• [x] Create SVGClipPathElement, see https://drafts.fxtf.org/css-masking-1/#ClipPathElement
  • [x] Attributes: clipPathUnits = "userSpaceOnUse | objectBoundingBox"
  • Default is userSpaceOnuse
• [x] Support for the clip-rule property
• [x] Make SVGClipPathElement non-renderable:

• handle.emplace<components::RenderingBehaviorComponent>(
  components::RenderingBehavior::Nonrenderable);

[jwmcglynn]

https://github.com/jwmcglynn/donner/commit/cd52962919525d68c3c337e88fb0cba75602015f is the start, but it has lots of failing tests in resvg_test_suite.cpp:

https://github.com/jwmcglynn/donner/blob/cd52962919525d68c3c337e88fb0cba75602015f/donner/svg/renderer/tests/resvg_test_suite.cc#L208-L243

[jwmcglynn]

https://github.com/jwmcglynn/donner/pull/171 adds clip-rule support