RenderTarget: Fix copy of images.

[Mugen87]

Fixed #30540.

Description

Second attempt of #30570, now with a note in the documentation.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.65 78.39	336.65 78.39	+0 B +0 B
WebGPU	522.23 144.94	522.23 144.94	+0 B +0 B
WebGPU Nodes	521.7 144.84	521.7 144.84	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.64 112.24	465.7 112.26	+55 B +21 B
WebGPU	592.61 160.56	592.66 160.58	+55 B +17 B
WebGPU Nodes	547.74 150	547.79 150.02	+55 B +14 B

[gkjohnson]

Looks great, thank you!