Normalizes a LinkMarker into a concrete LinkMarkerRecord. Looks
up a built-in name ('arrow', 'circle', …) in the marker registry, passes a
custom record through unchanged, and returns null for 'none', undefined,
or an unknown name, meaning "draw no marker".
Normalizes a LinkMarker into a concrete LinkMarkerRecord. Looks up a built-in name (
'arrow','circle', …) in the marker registry, passes a custom record through unchanged, and returnsnullfor'none',undefined, or an unknown name, meaning "draw no marker".