chore(types): add back ReactThreeFiber namespace, math types

[CodyJasonBennett]

Continues #2672. Related: #2668.

[CodyJasonBennett]

Need to double check Layers' usage.

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[krispya]

Need to double check Layers' usage.

What do you mean by Layer usage? I can check some cases for you.

[CodyJasonBennett]

I'm not sure how to use it, we have no coverage for it in tests for applyProps and don't want it to slip.

[krispya]

Do you mean THREE.Layers like this example? https://github.com/pmndrs/react-three-fiber/blob/master/example/src/demos/Layers.tsx

[krispya]

Following up on this. It looks good in my basic tests so far, but I have not tested layers.

[CodyJasonBennett]

Looks like master resolves to number | THREE.Layers, accepting a scalar type rather than a single element array. This would be more correct.