Remove CutlineBbox module in favor of upstream ClipExtension?

[kylebarron]

I don't think we need both

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CutlineBbox vs deck.gl's ClipExtension

They do the same job, in different reference frames — both correct under auto-offset.

• CutlineBbox captures the raw positions.xy attribute (absolute common space) and
  compares against an absolute-common-space bbox that's projected once at definition
  time (pass-through getUniforms).
• ClipExtension (fragment path) captures geometry.position.xy, which under
  WEB_MERCATOR_AUTO_OFFSET (zoom ≥ 12) is camera-relative / offset common space
  (project.glsl subtracts coordinateOrigin). Its draw() then re-projects clipBounds
  through this.projectPosition(...), and project-functions.js applies the same offset
  subtraction in offsetMode. So both sides carry the offset and it cancels — clipping
  stays correct at every zoom.

The CutlineBbox comment ("capture raw positions to keep the test stable across zoom") was
avoiding the failure mode of comparing offset positions against an un-offset bbox.
ClipExtension simply offsets both sides instead. Both are valid; if anything
ClipExtension's small camera-relative magnitudes are marginally more float-friendly at the
clip edge.

ClipExtension already works end-to-end on COGLayer — the vermont example proves it
(extensions: [new ClipExtension()] is auto-forwarded down the composite hierarchy to the
mesh sublayer).

What CutlineBbox does that ClipExtension doesn't: essentially nothing for this use
case. Both handle only axis-aligned rectangles (USGS quads are axis-aligned in common space).
The only differences are ergonomic:

	CutlineBbox	ClipExtension
API	typed RasterModule in renderPipeline	extensions + clipBounds, needs @ts-expect-error
Gotcha	none	must set clipByInstance: false (auto-detect sees instancePositions)
Per-frame	pass-through	2-point reproject (negligible)
Maintained by	us	deck.gl

Recommendation: deprecate CutlineBbox. deck.gl ships an equivalent we already use;
maintaining a redundant shader module + its tests + docs isn't worth it, and we're pre-1.0 so
removing a gpu-modules export is cheap. The only wart on the ClipExtension side is the
clipBounds typing cast and the clipByInstance: false footgun — both of which we could
smooth with a tiny typed helper if we want.