Fix parsing of css font strings

[weskamm]

Description

This fixes the parsing of the css font string coming from openlayers. Before this change, some font properties were not or wrongly detected, as the parsing did not follow the spec.

@geostyler/devs please review

Related issues or pull requests

Please list issues or pull requests that the changes you propose are related to. It does not matter if they are still open and/or unmerged, any link is appreciated.

Pull request type

Please check the type of change your PR introduces:

• [x] 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
• [x] No
• [ ] I am unsure (no worries, we'll find out)

Checklist

• [x] I understand and agree that the changes in this PR will be licensed under the BSD 2-Clause License
• [x] I have followed the guidelines for contributing
• [x] The proposed change fits to the content of the code of conduct
• [x] 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!