form elements of type 'hidden' or 'value' cause an empty TD in a 'table' element

Problem/Motivation

If a form element has '#type' => 'table', then its child elements become the table rows, and its grandchild elements become the table cells.

If an element is of type hidden or value like this:

      $element[ROW][CELL] = [
        '#type' => 'value',
        '#value' => 42,
      ];

then it is not shown to the user.

However, in both cases, an empty cell is created.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet