WebGPUBackend: Fix manual clear() regression.

[Mugen87]

Related issue: #30647

Description

While investigating #31387, I've noticed that #30647 has introduced a minor regression in WebGPUBackend.clear() when rendering directly to the default framebuffer (e.g. when using THREE.LinearSRGBColorSpace as the output color space). Below fiddles demonstrates the glitch:

https://jsfiddle.net/5k3xga61/

The default render pass descriptor is shared so it is not possible to rely on cached depth and stencil clear values in clear(). They must be configured on every clear invocation or the configuration values in the depth stencil attachment are incorrect.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	338.37 78.95	338.37 78.95	+0 B +0 B
WebGPU	557.72 154.42	557.67 154.41	-50 B -13 B
WebGPU Nodes	556.64 154.2	556.59 154.19	-50 B -13 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	469.6 113.66	469.6 113.66	+0 B +0 B
WebGPU	633.39 171.45	633.34 171.44	-50 B -13 B
WebGPU Nodes	588.52 160.8	588.47 160.79	-50 B -13 B

[RenaudRohlinger]

Oops sorry about that!