Calls to the prototype inference API can take several seconds, and we currently have no visual feedback telling the user that anything is happening. We should replace the results area with a spinner while waiting for the API response.

• ToolHolder should listen to the query-begin event that will be introduced after merging the pull request for T276840.
• The listener will set this.result to null, which clears the results pane.
• A loading indicator, such as anything on this page, is superimposed over the results area or attached to the submit button.
• The submit button should be disabled during load.
• Clean up loading indicators in response to the query-results event.
• Handle network errors and timeout, without leaving the interface in a "loading" or disabled state.