fix: Revert back to boolean type for experimental-ivy flag

This flag was accedentally changed to an array in
440a6c6
It needs to be only a boolean so that it stays a checkbox in the UI.

Author: atscott

package.json

@@ -178,4 +178,4 @@
     "type": "git",
     "url": "https://github.com/angular/vscode-ng-language-service"
   }
-}
+}