Renderer: Disable autoClear in the output pass.

[Mugen87]

Related issue: #30450

Description

As stated in the existing comment in Renderer.clear(), a clear operation should only affect the internal intermediate render target and not the canvas framebuffer. However, when autoClear is enabled, the output pass will clear the canvas which breaks multi-view rendering: https://jsfiddle.net/tea4dchg/

The PR fixes the issue by disabling auto clear and also moves the output pass related logic into an own method.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.12 78.22	336.12 78.22	+0 B +0 B
WebGPU	517.05 143.52	516.99 143.53	-67 B +12 B
WebGPU Nodes	516.52 143.42	516.45 143.43	-67 B +11 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.17 112.09	465.17 112.09	+0 B +0 B
WebGPU	589.05 159.72	588.99 159.73	-67 B +11 B
WebGPU Nodes	544.42 149.28	544.35 149.28	-67 B +10 B