Function load_next_js_template 

pub async fn load_next_js_template<'b>(
    template_path: &'b str,
    project_path: FileSystemPath,
    replacements: impl IntoIterator<Item = (&'b str, &'b str)>,
    injections: impl IntoIterator<Item = (&'b str, &'b str)>,
    imports: impl IntoIterator<Item = (&'b str, Option<&'b str>)>,
) -> Result<Vc<Box<dyn Source>>>

Loads a next.js template, replaces replacements and injections and makes sure there are none left over.