fix: add caching to PostCSS for regular stylesheets

[markdalgleish]

For now this is focused on regular stylesheets. Future PRs will extend this to more PostCSS touch points.

This PR introduces a generic file watch cache that can be used to cache async file processing and invalidate cache entries whenever relevant files are changed. I've integrated this into both old and new dev servers, and for consistency I've also integrated it into the build process so that plugins don't need to behave differently between dev and build and can always assume the presence of the cache.

Note that our watcher logic in watch.ts needed to be patched so that watch paths are always absolute. I've added a comment explaining why this is the case, but basically we need to always watch absolute paths so that Chokidar provides absolute paths in change events, which is important to ensure consistent values for the cache.

To test this, I've added some more complex PostCSS usage to our HMR test.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8f8c3aa

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

This PR includes changesets to release 18 packages

Name	Type
@remix-run/dev	Major
create-remix	Major
@remix-run/css-bundle	Major
remix	Major
@remix-run/architect	Major
@remix-run/cloudflare	Major
@remix-run/cloudflare-pages	Major
@remix-run/cloudflare-workers	Major
@remix-run/deno	Major
@remix-run/eslint-config	Major
@remix-run/express	Major
@remix-run/netlify	Major
@remix-run/node	Major
@remix-run/react	Major
@remix-run/serve	Major
@remix-run/server-runtime	Major
@remix-run/testing	Major
@remix-run/vercel	Major

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[jacob-ebey]

I like the cache abstraction, should serve us well.

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-70cc627-20230602 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version 1.17.0-pre.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[github-actions]

🤖 Hello there,

We just published version 1.17.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!