Disabled state

[emteknetnz]

Need to support a disabled state which is set via ->setDisabled(true)

This is similar though not quite the same as ->setReadonly() which had supported on this card

For example, with very quick test locally shows that there is a mouse pointer with the readonly field, though there isn't one with the disabled field

    public function getCMSFields()
    {
        $fields = parent::getCMSFields();
        $fields->insertAfter('Content', new TextField('MyText01'));
        $fields->insertAfter('Content', (new TextField('MyText02'))->setReadonly(true));
        $fields->insertAfter('Content', (new TextField('MyText03'))->setDisabled(true));
        return $fields;
    }   

Some differences between readonly and disabled can be found here

Acceptance criteria

• When setDisabled is set to true, the field renders with the read only styles and the user can not update the value.
• There's a follow up card to block any updates in the backend for readonly/disabled field.

Notes

• We discussed whether disabled or readonly should have any practical difference. We concluded it wasn't really worth treating them as separate use cases.

PR

• https://github.com/silverstripe/silverstripe-linkfield/pull/189

[sabina-talipova]

PR is merged. Task is completed.