Add Export Files Feature to Three.js DevTools

[RuthySheffi]

This pull request introduces an export files feature to the Three.js DevTools extension.

Key updates include:

• Added export-handler logic to enable exporting scenes and assets directly from the DevTools panel.
• Integrated new UI elements and icons for export actions.
• Updated content script and panel logic to support export requests and communication.
• Added devtools in utils to copy build files and GLTFExporter to the extension folder.
• Updated the manifest for to run devtools.

This feature streamlines the workflow for developers working with Three.js by making it easier to export and share assets during development.

Please review and let me know if any changes are needed!

[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	553.64 153.44	553.64 153.44	+0 B +0 B
WebGPU Nodes	552.99 153.28	552.99 153.28	+0 B +0 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	628.6 170.13	628.6 170.13	+0 B +0 B
WebGPU Nodes	583.45 159.47	583.45 159.47	+0 B +0 B