feat: 2034 - "just holes" polygon feature

[monsieurtanuki]

What

• Introduced a bool justHoles field for polygon:
  • the "full" points won't be considered and will be replaced by the full map
  • the "holes" points will be considered as the only "not colored" parts of the polygon
• New example named "Advanced polygons".
• The typical use-case would be using a single polygon with several holes.
• In that case only the holes are clickable.
• Could be that eventually we may consider that feature to be applied to the map instead, and have all polygons considered as holes. The thing is that currently we cannot say: "just hit hole number 2", because the label is attached to the "polygon", and all holes share the same polygon.
• cc @enricostrijks and Provide option for Polygons & Polylines not to render shortest path over anti-meridian #2034

Screenshots

new menu item	example

multi-world example	hit example

Files

New file:

• advanced_polygons.dart: Example dedicated to polygons with advanced features.

Impacted files:

• main.dart: added the new AdvancedPolygonsPage page
• menu_drawer.dart: added the new AdvancedPolygonsPage page
• painter.dart: managed the justHoles case; refactored a bit borderPaint
• polygon.dart: added the bool justHoles field
• polygon_layer.dart: special case for justHoles
• projected_polygon.dart: special case for `justHoles

[enricostrijks]

LGTM