integration: Split out compiler into @vanilla-extract/compiler package

[askoufis]

There's a few things that motivated me to do this split:

1. All bundler plugins depend on the integration package, which means they all and up pulling in vite and vite-node dependencies, yet most bundler integrations don't use the compiler yet. Splitting out the compiler into a separate package means these dependencies aren't installed in bundler integrations that don't use the compiler.
2. A separate, 0-versioned compiler package allows less disruptive (less major versions) API iteration on the compiler. Although we don't care that much about major versions in the integration package, I still feel like the compiler's API and implementation is unstable enough that it should be treated as such. Isolating it in a separate package helps with this.

At a point in the future, it may make sense to merge the compiler back into the integration package.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9cda792

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

This PR includes changesets to release 9 packages

Name	Type
@vanilla-extract/vite-plugin	Patch
@vanilla-extract/compiler	Minor
@vanilla-extract/integration	Major
@vanilla-extract/esbuild-plugin	Patch
@vanilla-extract/jest-transform	Patch
@vanilla-extract/parcel-transformer	Patch
@vanilla-extract/rollup-plugin	Patch
@vanilla-extract/webpack-plugin	Patch
@vanilla-extract/next-plugin	Patch

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