src/language-handlebars/printer-glimmer.js/printOpenBlock
function printOpenBlock(path, print) {
  const node = path.getValue();

  return group(
    concat([
      printOpeningBlockOpeningMustache(node),
      printPathAndParams(path, print),
      printBlockParams(node.program),
      softline,
      printOpeningBlockClosingMustache(node),
    ])
  );
}