Docs: Add code copy button.

[Mugen87]

Related issue: -

Description

This PR adds the copy button to code sections in the new JSDoc template.

BTW: I was wondering why the current docs did not show the buttons at https://threejs.org/docs until I noticed the respective images are not hosted on GitHub pages. Fixed via faa899d.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	336.64 78.39	336.64 78.39	+0 B +0 B
WebGPU	522.6 145.08	522.6 145.08	+0 B +0 B
WebGPU Nodes	522.07 144.98	522.07 144.98	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	465.69 112.26	465.69 112.26	+0 B +0 B
WebGPU	593 160.69	593 160.69	+0 B +0 B
WebGPU Nodes	548.13 150.12	548.13 150.12	+0 B +0 B

[mrdoob]

Would it be possible to post screenshots in these PRs so we can see how things are looking without having to open a terminal and run the script? Only when it makes sense that is.

[Mugen87]

Understood!

In this particular case, I was talking about the button on the top-right of a code section: