Add support for vanilla Three.js

[nwpointer]

Vanilla support was rolled back with most recent large release. Consider supporting vanilla apps and so it can be used in frameworks other than r3f such as threlte.

[LDC-ar]

I'd love to see vanilla support. Since vanilla is the base of everything, no matter if the framework doesn't exist anymore in the future.

[jerzakm]

I'd also be interested in this. I didn't look too much into the code, but would it be possible to keep core mechanics in vanilla Three and then have r3f as a wrapper?

[nwpointer]

This should now be possible but I've not tested it personally after the release of this PR: #30