Enable Prefill Required Attributes setting

This adds a new experimental setting for prefilling required attributes as blocks are completed from intellisense. For example, completing a resource provider will fill in the required attributes automatically.

package.json

@@ -184,6 +184,11 @@
               "scope": "resource",
               "type": "boolean",
               "default": false
+            },
+            "prefillRequiredFields": {
+              "scope": "resource",
+              "type": "boolean",
+              "default": false
             }
           }
         }