WebGLGeometries: Announce stop of THREE.Geometry support.

[Mugen87]

Instead of directly stop rendering THREE.Geometry (see #15514), it might be more acceptable to announce this change so users can easier prepare for it.

The warning is logged once for each automatic geometry conversion of WebGLRenderer.

[looeee]

I'd say we should give at least 6 months warning.

Once we get treeshaking working, most of the unused code like this should be taken out of user's bundles, right?

[Mugen87]

Once we get treeshaking working, most of the unused code like this should be taken out of user's bundles, right?

Not sure what you mean. Are you referring to the console.log?

[looeee]

No, I mean the actual Geometry classes.

For example BoxGeometry.js has two exports:

export { BoxGeometry, BoxBufferGeometry };

When a user does this:

import { BoxBufferGeometry } from 'three';

...they currently get both exports included in their bundle (well actually, they get all the exports from three.module.js) . With tree shaking, the BoxGeometry class should get identified as dead code and removed along with all the other unused classes.

[Mugen87]

Ah, now I see what you mean. Yes, this is the intended outcome!

[Mugen87]

Closing for now. I should have created this PR as a "Draft PR" since I primarily wanted some feedback about this approach. As soon as @mrdoob feels comfortable with deprecating Geometry, we can add such a message until it the code paths are finally removed.