Add a job for vscode extension

.gitlab-ci.yml

@@ -199,3 +199,16 @@ pages-attempt:
   only:
     - merge_requests
     - /^.*-run-dev$/
+
+vscode-extension:
+  extends: .nix
+  only:
+    - merge_requests
+    - dev
+    - /^.*-run-dev$/
+  script:
+    - nix-build tools/lsp -A ligo-vscode-extension
+    - cp -Lr --no-preserve=mode,ownership,timestamps result/*.vsix ligo-extension.vsix
+  artifacts:
+    paths:
+      - ligo-extension.vsix