fix: uniforms have stable refs for ShaderMaterial

[krispya]

Currently, if a uniform is recreated due to a rerender or simply an HMR and the uniform is passed in as a prop, then it overwrites the uniforms object.

// This will still regenerate on HMR
const uniforms = useMemo(() => {}, [])

// Overwrites the original reference
return <shaderMaterial uniforms={uniforms} />

This is catastrophic for Three which assumes this object never changes in its program caching. This leads people to do silly things like put Math.random() in the key prop forcing the material itself to regenerate every rerender.

This change makes the uniforms objects on ShaderMaterial and its derivatives have a stable reference. Anything passed into uniforms will instead copy into it. This is the same as behavior for math structures that have copy such as position, rotation, quaternion, etc.

The user would then get the uniforms ref from the material ref itself.

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