code: function addTemplateToCompiler (mainCompiler, templatePath) {
    const childCompiler = getChildCompiler(mainCompiler);
    const isNew = childCompiler.addTemplate(templatePath);
    if (isNew) {
      clearCache(mainCompiler);
    }
  }
docs: Register a template for the current main compiler
  @param {WebpackCompiler} mainCompiler
  @param {string} templatePath