Restructure Shader Composer

[hmans]

See #362

Issues:

• Extract Shader Composer core that doesn't rely on Three.js #362

Extra Checklist:

• Rename $vec3() et al back to vec3()? It feels more natural.

[codesandbox]

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[changeset-bot]

🦋 Changeset detected

Latest commit: b98a31c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 15 packages

Name	Type
shader-composer	Major
@shader-composer/core	Major
@shader-composer/noise	Major
@shader-composer/postprocessing	Major
@shader-composer/r3f	Major
@shader-composer/three	Major
shader-composer-toybox	Major
material-composer	Minor
@material-composer/patch-material	Minor
material-composer-r3f	Minor
render-composer	Minor
vfx-composer	Minor
vfx-composer-r3f	Minor
@material-composer/patched	Patch
r3f-stage	Patch

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