Function fallback_prompt_renderer 

pub fn fallback_prompt_renderer(
    level: PromptLevel,
    message: &str,
    detail: Option<&str>,
    actions: &[PromptButton],
    handle: PromptHandle,
    window: &mut Window,
    cx: &mut App,
) -> RenderablePromptHandle

Use this function in conjunction with App::set_prompt_builder to force GPUI to always use the fallback prompt renderer.