Orbital Controls modes of input to accomodate null values

[Heaust-ops]

So say I want left click to control nothing.
Right now I have to do this,

    controls.mouseButtons = {
      LEFT: null as unknown as THREE.MOUSE,
      MIDDLE: THREE.MOUSE.ROTATE,
      RIGHT: THREE.MOUSE.LEFT,
    };

This PR tells typescript to expect null values when the dev wants a specific mode of input not to control anything.
'null' is probably better than making it optional / undefined because it's explicit and fields can unknowingly be left undefined.

[joshuaellis]

Can you point to the THREE documentation // src code where this type change should be allowed?

[Heaust-ops]

Yeah, orbital controls handles these options with switch case,
like in line 868 in OrbitControls.js,
a default case is handled, that means anything other than the expected value, like null, is handled,
and in such a case (unexpected value, like null), the orbital controls won't do anything, or sit idle, line 947.
which is exactly what we want, for them to sit idle on null.

[joshuaellis]

closed in favor of #236