[fix] Restore support for rendering custom fieldsets on 'joomla.edit.params'. Fixes #4284

Retrieve all fieldsets instead of params and attribs only

Define ignore_fieldsets consistently

Add ignore_fieldsets

Code style

Further implementation of ignore_fieldsets

Restore options tabs in com_content

Update modal.php with related changes to restore support for rendering custom fieldsets when using JLayout 'joomla.edit.params'

Update modal.php with related changes to restore support for rendering custom fieldsets when using JLayout 'joomla.edit.params'