[v9] experiment(types): ThreeElements extends interface extends mapped type

[CodyJasonBennett]

Tries to address an issue in #2668 (comment) where writing into ThreeElements completely overwrites it.

declare module '@react-three/fiber' {
  interface ThreeElements {
    element: ThreeElement<typeof Element>
  }
}

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[krispya]

This isn't required as long as the project has an up-to-date version of TypeScript: #2668 (comment)