Add a more detailed type definition for WebMercatorViewport.getLocationAtPoint()

[sangaline]

The type definition for WebMercatorViewport.getLocationAtPoint() currently uses implicit any typing for lngLat and pos. This can cause TypeScript build errors if noImplicitAny is enabled and skipLibCheck is disabled:

node_modules/@math.gl/web-mercator/src/web-mercator-viewport.d.ts:149:23 - error TS7031:
Binding element 'lngLat' implicitly has an 'any' type.

149   getLocationAtPoint({lngLat, pos}): number[];

node_modules/@math.gl/web-mercator/src/web-mercator-viewport.d.ts:149:31 - error TS7031:
Binding element 'pos' implicitly has an 'any' type.

149   getLocationAtPoint({lngLat, pos}): number[];

This PR is a one-line change to add types for these arguments. The type signature for the function now matches the non-legacy WebMercatorViewport.getMapCenterByLngLatPosition() method (visible a few lines up in the diff). The legacy function simply calls and returns the non-legacy method with the same arguments, so these should have the same type signature:

  // Legacy method name
  getLocationAtPoint({lngLat, pos}) {
    return this.getMapCenterByLngLatPosition({lngLat, pos});
  }

[CLAassistant]

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