Sub-RadioButton-Element located in container does not support clientside required validation

Problem/Motivation

Sub-RadioButton-Element located in container(hidden/visible by condition) does not support clientside required validation
※By the way,this bug will not happend when parent container is always visible

Steps to reproduce

1）Import attachment[webform.webform.sub_element_require_test_radiobu.yml] into drupal site.
2) Access the webform page that you imported in step1
3) Click submit button，request could not be submitted due to clientside required validation of [RadioButton]
4) Make [RadioButton] check on
5) Click submit button，request will be submitted without clientside required validation of [Sub-RadioButton]

Proposed resolution

If you have done blew step Before Step 5, the clientside required validation of [Sub-RadioButton] will be run.
4-1) Make [Trigger] check out
4-2) Make [Trigger] check on
The reason for this phenomenon is that when [Trigger] is be checked on, the [Sub-RadioButton] is added with the correct required tag by JS.
So,I think we need to make sure that when PHP does the page init rendering, the HTML of the [Sub-RadioButton] is rendered correctly.

Remaining tasks

Write patch
Review patch
Commit patch

User interface changes

API changes

Data model changes