Allow Signature Element To Notify Value Changes And Work With Webform Conditions.

Problem/Motivation

Currently, the Signature element doesn't support Webform Conditions or ajax value change events.

Steps to reproduce

1. Create a new webform, add a Signature element and a Text field element

2. Make the Text field Visible condition depend on wether the Signature element is filled or empty

3. The condition doesn't work (neither do ajax events, etc.)

Proposed resolution

Trigger the change event when updating the associated input field value on webform.element.signature.js line 56.

Remaining tasks

I'm attaching a .patch that works on webform v6.2.9.

It if it's appropriate perhaps make the change in the dev branch of webform.