Compute multiFeatureLocation in addition to location property in @turf/nearest-point-on-line

[EmilJunker]

This adds a multiFeatureLocation property to the points returned by the nearestPointOnLine function. If there is just one LineString, then this will be the same as the existing location property. But if you pass a MultiLineString, this will tell you the distance along the line between the start of the MultiLineString where the closest point was found and the closest point itself. See #2753 for an example why this is useful.

Closes #2753.

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