feat: add vector3ToLatLngAltitude conversion

[telmon95]

Summary

• Adds vector3ToLatLngAltitudeRelative (inverse of latLngToVector3Relative) and ThreeJSOverlayView.vector3ToLatLngAltitude() (accounts for anchor + upAxis)
• Includes round-trip unit tests using the NYC examples from the issue discussion
• Documents the inverse API in the README and removes the stale latLngToVector3 import from the example

Fixes #887

Test plan

• npm run lint
• npm test (55 tests passing)
• Confirm round-trip: overlay.vector3ToLatLngAltitude(overlay.latLngAltitudeToVector3(coords)) ≈ original coords for default and upAxis: "Y"
• Spot-check against a map click listener near and far from the anchor

[google-cla]

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