[Bug] `Layer.getBounds()` type is not compatible with `WebMercatorViewport.fitBounds()`

Description

If one looks at the the fitBounds docs, the example usage is the following:

const [initialViewState, setInitialViewState] = useState<MapViewState>({
  longitude: -100,
  latitude: 40,
  zoom: 4
});
const [hasLoaded, setHasLoaded] = useState<boolean>(false);

const layer = new ScatterplotLayer({...});

const onAfterRender = () => {
  if (!hasLoaded && layer.isLoaded) {
    setHasLoaded(true);

    const viewport = layer.context.viewport as WebMercatorViewport;
    const {longitude, latitude, zoom} = viewport.fitBounds(layer.getBounds());
    setInitialViewState({longitude, latitude, zoom});
  }
};

However, the return type of ScatterPlotLayer.getBounds() will be [number[], number[]] | null, while WebMercatorViewport.fitBounds takes in a [[number, number], [number, number]]. The example code fails to type check as a result of this issue both because layer.getBounds() could return null and because number[] cannot be coerced to [number, number]. The first issue is easy to fix with a null check, but the second requires either an as cast or some more arduous checks.

Flavors

• Script tag
• React
• Python/Jupyter notebook
• MapboxOverlay
• GoogleMapsOverlay
• CartoLayer
• ArcGIS

Expected Behavior

If the output of Layer.getBounds() is truthy, its type should be accepted in WebMercatorView.fitBounds().

Steps to Reproduce

Follow the instructions on the fitBounds() docs to set up a Deck.GL scene.

Environment

• Framework version: 8.9.6
• Browser: Chrome
• OS: MacOs

Logs

No response

Start with the TypeScript declarations for Layer.getBounds() and WebMercatorViewport.fitBounds(), using the fitBounds documentation example as the reproduction. Check the non-null getBounds() result and verify that its tuple type is accepted by fitBounds without casts or element-by-element checks.