Code split CSS chunks

[itsdouges]

Closes #722

Seems to work, need to think about edge cases. As well as what happens with multiple entry points. This might also closes #669 as we remove the need for placing everything into a single style sheet via cache groups.

@jantimon how's this look?

Changes

• Compiled now supports async CSS chunks
• To enable this Compiled now takes control over the entire CSS pipeline
• Any CSS declared inside or outside of Compiled will be sorted and potentially hoisted if unsafe for atomic styles

TODO

• Investigate potential edge cases & side effects
• Update docs to talk through how Compiled will take control of the entire CSS pipeline

[changeset-bot]

🦋 Changeset detected

Latest commit: 0768f8e

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

This PR includes changesets to release 3 packages

Name	Type
@compiled/webpack-loader	Minor
@compiled/css	Minor
@compiled/babel-plugin	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[cloudkite]

Nice work!! Does this enable multiple entry points? Not sure how common this is in the wild, but our app uses multiple entry points to build bundles for independent apps (website, chrome extension, embed etc) within a monorepo. Being able to only include styles used for a particular entry point would be great!

[itsdouges]

Hi! Yeah exactly, need to investigate what happens and probably tweak it 🙂

[itsdouges]

Closing, this can be used as a reference when picking it up later.