Discrepancy in unsized DEPTH_STENCIL handling between Firefox and Chrome

[kenrussell]

In mrdoob/three.js#16756 it was pointed out that Firefox's WebGL 2.0 implementation seems to be allowing the unsized DEPTH_STENCIL format as an argument to renderbufferStorageMultisample, while Chrome's implementation rejects it.

WebGL 2.0 and OpenGL ES 3.0 tightened the rules around texture and renderbuffer format specification so a test should be written to make all implementations behave identically. Ideally it would be an error to specify the unsized DEPTH_STENCIL format in WebGL 2.0.

CC @jdashg

[kdashg]

We process renderbufferStorage as renderbufferStorageMultisample(samples=0), so I'd prefer to Chrome to expand what it accepts for renderbufferStorageMultisample, and maintain this layered structure of these entrypoints.

[kdashg]

This is easy enough to fix I guess.