Add complete support for OpenLayers flat style format

[LHBruneton-C2C]

Description

Implements #841

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!

TO REVIEW

• Confirm FlatStyleArray as Symbolizers
• Confirm that rotation needs / Math.PI * 180
• Confirm when to use or not use structuredClone

TODO

• dynamic text label
• unsupported properties
• property-based filter
• boolean function
• case function
• nested function
• pi <=> 3.141592653589793
• distinguish simple stroke from fill with outline