[4.0][a11y] Labels Module Assignment are not associated with forms

[zwiastunsw]

Steps to reproduce the issue

1. Go to Modules new/edit
2. Use screen reader (I use NVDA), move focus to Module Assignment field
   or
3. Click on the Module Assignment label
   or
4. Check Accessibility tree (in Chrome)

Expected result

• The screen reader should announce the role combobox and the label Module Assignment
• When you click on a label, the field should receive a focus
• The field should have an accessible name in the Accessibility tree

Actual result

1. Screen reader (NVDA) announces only a role, does not announce a label
2. When you click on a label, the field does not receive a focus
3. The field does not have an accessible name in the Accessibility tree

System information (as much as possible)

• Windows 10,
• Chrome 72.0.3626.81, Firefox/65.0
• Apache 2.0 server (online)

Additional comments

The label should probably be assigned to the 'select' field.

[brianteeman]

Please test #23922

[joomla-cms-bot]

Set to "closed" on behalf of @Quy by The JTracker Application at issues.joomla.org/joomla-cms/23889