WebGPUBackend: Fix generateMipmaps when used copyFramebufferToTexture()

[sunag]

Fixes #31143

Description

copyFramebufferToTexture() is not generating mipmaps after copying even if the property texture.generateMipmaps is true.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	337.26 78.64	337.26 78.64	+0 B +0 B
WebGPU	551.52 152.93	551.58 152.94	+56 B +4 B
WebGPU Nodes	550.88 152.78	550.93 152.78	+56 B +4 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	468.44 113.28	468.44 113.28	+0 B +0 B
WebGPU	626.53 169.61	626.59 169.62	+56 B +4 B
WebGPU Nodes	581.38 158.94	581.44 158.94	+56 B +4 B

[ycw]

This PR generated mipmaps twice, L2359, L2399 ?

[sunag]

This PR generated mipmaps twice, L2359, L2399 ?

Fixed