Fix support for scss in static build

[matthewp]

Changes

• Previously the static build would fail to compile CSS supersets like scss because it was extracting dependencies and adding them back as imports. Since these deps were scss themselves, the CSS wouldn't load.
• This brings things back to the way that they were before; CSS is completely compiled in the compiler, including dependencies.
• Instead, we extract dependencies to track via HMR. When HMR occurs we invalidate our compilation cache so that the root .astro styles are reloaded.

Testing

No HMR unit tests exists, tested via the example app (update is included here).

Docs

Bug fix only

[changeset-bot]

🦋 Changeset detected

Latest commit: 55ed808

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

This PR includes changesets to release 1 package

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astro	Patch

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[jonathantneal]

CSS is completely compiled in the compiler, including dependencies.

Is the CSS always processed by PostCSS (or the appropriate superset parser)? If not, may it be? I think this is critical. I believe we cannot support every possible superset without a conforming parser, and the (previous?) internal one (written in Go?) breaks a lot of valid CSS, including container queries.

[matthewp]

Is the CSS always processed by PostCSS (or the appropriate superset parser)? If not, may it be? I think this is critical. I believe we cannot support every possible superset without a conforming parser, and the (previous?) internal one (written in Go?) breaks a lot of valid CSS, including container queries.

Yes, this doesn't change how compilation works. The Go compiler calls out to JS and that's what CSS compiling actually occurs. I should have said that it happens "in the compilation" step instead of in the compiler.

[jonathantneal]

Excellent. Thanks for the clarification. 👍