fix(useLoader): make better use of generics for extensions

[CodyJasonBennett]

Fixes #2579 by inferring the loader prototype and passing it to extensions.

import { useLoader } from '@react-three/fiber'
import { MTLLoader, OBJLoader } from 'three-stdlib'

const materials = useLoader(MTLLoader, '/path/to/materials.mtl')
const object = useLoader(OBJLoader, '/path/to/geometry.obj', (loader) => {
  materials.preload()
  loader.setMaterials(materials)
})

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit a9e6db6:

Sandbox	Source
example	Configuration

[CodyJasonBennett]

Will need to evaluate upstream effects in Drei before merging.