Add support for basic addVariant plugins with new @plugin directive (#13982)

* Add basic `addVariant` plugin support

* Return early

* Load plugins right away instead later

* Use correct type for variant name

* Preliminary support for addVariant plugins in PostCSS plugin

* Add test for compounding plugin variants

* Add basic `loadPlugin` support to Vite plugin

* Add basic `loadPlugin` support to CLI

* add `io.ts` for integrations

* use shared `loadPlugin` from `tailwindcss/io`

* add `tailwindcss-test-utils` to `@tailwindcss/cli` and `@tailwindcss/vite`

* only add `tailwindcss-test-utils` to `tailwindcss` as a dev dependency

Because `src/io.ts` is requiring the plugin.

* move `tailwindcss-test-utils` to `@tailwindcss/postcss `

This is the spot where we actually need it.

* use newer pnpm version

* Duplicate loadPlugin implementation instead of exporting io file

* Remove another io reference

* update changelog

---------

Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: pnpm/action-setup@v3
         with:
-          version: ^8.15.0
+          version: ^9.5.0
 
       - name: Use Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v3

.github/workflows/release.yml

@@ -15,7 +15,7 @@ permissions:
 env:
   APP_NAME: tailwindcss-oxide
   NODE_VERSION: 20
-  PNPM_VERSION: ^8.15.0
+  PNPM_VERSION: ^9.5.0
   OXIDE_LOCATION: ./crates/node
 
 jobs: