Extending the SLD/SE rendering capabilities of Mark for more symbols and better area fill

[stephanr]

This PR is the, reworked, main part of the larger PR #1204 and includes #1420.

The following part are included:

• a new extension point, which allows implementing custom Graphic/Mark/WellKnownName handlers.
• (new) test cases which render a feature collection with a style and compare the results to the image
  • bbox is provided by the featurecollection, with and height is taken from the reference image
• corrections that improve the rendering of symbols for area fills
• documentation is reduced to the parts included in this pr
• the implementation for WellKnownName whit the prefixes shape://, extshape://, qgis:// and ttf:// do not include new or changed dependecies and are reworked versions from their geoserver/geotools counterpart (which is also LGPL 2.1 or newer)
  • see extshape:// shape:// qgis:// ttf:// (The references are to a newer version of geotools)
• include a helper function to calculate the size of an mark for simplified hatching
• as a result of these works the rendering of fill will look a little different
  • a comparison can be previed by looking at commit d0ab83a

[stephanr]

The PR was rebased to the current main, and also the obsolete change of ShapeStroke was removed.