Allow option to set SDF on a PointAnnotation image modifier using SwiftUI

[AppleJuiceBreak]

As far as I can tell when using SwiftUI with a PointAnnotation and the image(named: String) modifier there doesn't seem to be a way to enable SDF, not without tapping into MapViewReader.

If doing:

Map(viewport: $viewport) {
    PointAnnotationGroup(annotations, id: \.id) { annotation in
        PointAnnotation(coordinate: annotation.coordinates)
            .image(named: "marker-icon")
            .iconColor(.red)
    }
}

The icon color would of course not be red as SDF was not enabled. In this PR i've optionally added the ability to set SDF directly on the modifier

Map(viewport: $viewport) {
    PointAnnotationGroup(annotations, id: \.id) { annotation in
        PointAnnotation(coordinate: annotation.coordinates)
            .image(named: "marker-icon", sdf: true) // as long as the image is SDF enabled, the icon should now be red
            .iconColor(.red)
    }
}

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