Reusable workflow for publishing. (#64)

* Reusable workflow for publishing.

.github/workflows/publish.yml

@@ -0,0 +1,44 @@
+name: Publish to pub.dev
+
+## Caller of this workflow should use it as follows:
+## jobs:
+##   publish:
+##     uses: dart-lang/setup-dart/.github/workflows/publish.yml@main [or a recent commit hash / version tag]
+##     # with:
+##     #   working-directory: path/to/sub/directory
+
+on:
+  workflow_call:
+    inputs:
+      environment:
+        description: if specified, the workflow is required to be run in this environment (with additional approvals)
+        required: false
+        type: string
+      working-directory:
+        description: directory with-in the repository where the package is located (if not in the repository root)
+        required: false
+        type: string
+
+jobs:
+  publish:
+    name: 'Publish to pub.dev'
+    environment: ${{ inputs.environment }}
+    permissions:
+      id-token: write # This is required for requesting the JWT
+    runs-on: ubuntu-latest
+    steps:
+      # Checkout repository
+      - uses: actions/checkout@v3
+      # Setup Dart SDK with JWT token
+      - uses: dart-lang/setup-dart@7b1734b5b08d53fbf347cf96b664fa1a49cc6497
+      # Minimal package setup and dry run checks.
+      - name: Install dependencies
+        run: dart pub get
+        working-directory: ${{ inputs.working-directory }}
+      - name: Publish - dry run
+        run: dart pub publish --dry-run
+        working-directory: ${{ inputs.working-directory }}
+      # Publishing...
+      - name: Publish to pub.dev
+        run: dart pub publish -f
+        working-directory: ${{ inputs.working-directory }}