Write GraphicFill for PolygonSymbolizer

[jansule]

Description

This introduces the support for writing GraphicFill as part of a FillSymbolizer.

The main work was done by @rdewit in #244. I mainly did some minor refactorings and added tests.

Also, we now set the CanvasPattern directly as the color for the fill property, instead of using a custom renderer. Thereby we eliminate the z-index issue.

Please note that the common FillSymbolizer properties will have no effect, when using GraphicFill. This however is in line with the behavior in GeoServer.

Related issues or pull requests

Replaces #244
Solves #240
Solves #228

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Dependency updates
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe)
• I am unsure (we'll look into it together)

Do you introduce a breaking change?

• Yes
• No
• I am unsure (no worries, we'll find out)

Checklist

• I understand and agree that the changes in this PR will be licensed under the BSD 2-Clause License
• I have followed the guidelines for contributing
• The proposed change fits to the content of the code of conduct
• I have added or updated tests and documentation, and the test suite passes (run npm test locally)
• I'm lost; why do I have to check so many boxes? Please help!

[KaiVolland]

Nice work. Not sure if you want to resolve the commented TODOs before merging.
Please also check if geostyler-style still has to be transformed for jest.

[jansule]

Thanks for the reviews @KaiVolland @nevaldas!

Regarding the TODOs: I would rather keep them for now, as we have to check if we actually run into performance issues somewhere. For now, I would say it is ok as is.

[nevaldas]

We are using this already in our solution (yeah, we needed this ASAP). And the issue we had was that if image is not loaded when this code is executing, the getOlPatternFromGraphicFill returns null, meaning that image is not shown until map is refreshed. That happens when user moves the map, changes zoom level or can be forced via JS. This might be inconvenient. But in our case - I modified that line to check until image has loaded and force refresh of map (via JS). Sadly - that's not a global solution I could write here, as it requires access to the map class, which is not available from this part of code.

[KaiVolland]

Moved the discussion to issue #434