Add GitHub action to test and build extension

.github/workflows/package-vsix.yml

@@ -0,0 +1,39 @@
+name: Build and Test VS Code Extension
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+        node-version: [20]
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run tests
+        run: npm test:unit
+
+      - name: Build the extension
+        run: npx vsce package
+
+      - name: Upload .vsix artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: vscode-extension-${{ matrix.os }}
+          path: '*.vsix'