ColorLayer silently ignores pos/scale/parent transform

[obiot]

Problem

ColorLayer is constructed as super(0, 0, Infinity, Infinity) with the default 0.5 anchor. By the time ColorLayer.draw() runs, Renderable.preDraw has already translated by (-anchorX·width, -anchorY·height) = (-Infinity, -Infinity), leaving currentTransform.tx/ty non-finite.

Effects:

• Any user-set colorLayer.pos.set(...) is masked by the -Infinity translate.
• Nesting a ColorLayer inside a transformed Container (translate/scale/rotate) has no effect — the parent transform composes with -Infinity and stays non-finite.
• ColorLayer.draw() calls renderer.clipRect(0, 0, viewport.w, viewport.h). On WebGL this only "works" because of the non-finite-transform guard added in fix(clipping): correct Container.clipping under nested transforms (closes #1349) #1435 — it falls through to "no scissor", then clearColor paints the full framebuffer.

So ColorLayer is effectively a "fill the entire framebuffer with this color" command, not a positionable layer. The class API (pos, parent containers, etc.) suggests otherwise.

This came up while reviewing PR #1435 — a custom PartialColorLayer extends ColorLayer (used in the new clipping example) needed an explicit renderer.resetTransform() to make a sub-rect clipRect work, because the inherited -Infinity translate would otherwise turn the partial-band clip into a no-op.

Proposed fix

Honor pos/size. Drop super(0, 0, Infinity, Infinity) + 0.5 anchor in the constructor. New signature:

ColorLayer(name, color, z?, x?, y?, w?, h?)

• Defaults to viewport-sized (so the most common "full-canvas backdrop" case stays a one-liner).
• Anchor stays at (0, 0) so pos means top-left.
• draw() issues clipRect(0, 0, this.width, this.height) under the layer's own (finite) transform — sub-rect bands, transformed parents, and pos changes all just work.
• The clipping example's PartialColorLayer workaround can then be deleted.

Out of scope for #1435 (which is the clipRect fix). Happy to take this in a follow-up PR.