* move is* properties to prototypes and remove unused ones

* rebuild

* merge dev -> less-is

* remove rebuild from PR

* convert to ES modules

* rebuild

* move shaders back into glsl files

* reinstate polyfills

- Parameterized geometry (e.g. BoxGeometry) should not clone the base
properties of Geometry.
- CubeTexture: Clone is parameterless.

Provide a clone method to the specialized geometries in
src/extras/geometry, otherwise:
- the `.parameters` are not copied
- the `.type` of the clone is "Geometry" or "BufferGeometry"
- the cloned object is not an instance of the initial type. It loses its
specialization and becomes a plain `Geometry` or `BufferGeometry`.

Class deriving from `PolyhedronGeometry` defined  `this.parameters` all
over the place. Standardize to defining the `.type` and `.parameters`
after the `PolyhedronGeometry` constructor is called.

Also fix prototype inheritance chain for classes deriving from
`PolyhedronGeometry`.

Doesn't seem like we need a console log every time PlaneGeometry is used. Is PlaneGeometry really that bad?

Fixes #5570

Implemented Geometry2.merge().
Added offset and length parameters to Matrix3/Matrix4.applyToVector3Array().

Almost there...!

centroid was originally used by CanvasRenderer, now that it computes it as needed we don't need the bloat anymore.

Very much work-in-progress. This is going to take a while. Besides export being tedious by itself, I keep finding many things elsewhere in the codebase that need to be changed or fixed for something like this to work at all.