Add extension activation event for "Cargo.toml"

Author: Aidiakapi

package.json

@@ -34,7 +34,8 @@
     ],
     "preview": true,
     "activationEvents": [
-        "onLanguage:rust"
+        "onLanguage:rust",
+        "workspaceContains:Cargo.toml"
     ],
     "main": "./out/src/extension",
     "scripts": {