[openlayers] fix declaration for forEachSegment (#18816)

The declaration appears to be wrong (though I'm fairly new to TypeScript). For instance, the example at https://openlayers.org/en/latest/examples/line-arrows.html won't work like that.

types/openlayers/index.d.ts

@@ -3970,7 +3970,7 @@ declare module ol {
              * @template T,S
              * @api
              */
-            forEachSegment<T, S>(callback: (() => T), opt_this?: S): (T | boolean);
+            forEachSegment<T, S>(callback: ((this: S, start: ol.Coordinate, end: ol.Coordinate) => T), opt_this?: S): (T | boolean);
 
             /**
              * Returns the coordinate at `m` using linear interpolation, or `null` if no