code: function resolveDirectiveValue(directive, part) {
    // Directives are synchronous, so it's safe to read and delete value
    directive(part);
    const value = part._value;
    part._value = undefined;
    return value;
  }
docs: Resolve value of "directive"
  
  @param { function } directive
  @param { Part } part
  @returns { any }