[v9] feat(useLoader): support loader instances

[CodyJasonBennett]

Supports re-use of external loader instances:

import { GLTFLoader } from 'three-stdlib'
import { useLoader } from '@react-three/fiber'

const loader = new GLTFLoader()

function Model() {
  const gltf = useLoader(loader, '/path/to/model.gltf')
}

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