Allow to edit a TOSCA get function value in the Properties Assignment.

In the properties assignment view, when a property is selected that has a value set through the "TOSCA function" button, a "Clear Value" is displayed to reset the value to empty.

This behaviour shall be changed to show the "TOSCA functions" button instead. When selected, the modal used for setting the property using the TOSCA function shall be displayed containing the previously entered values.

The user shall be able to edit the previously entered values.

A "Clear value" button shall be added to the modal to remove the previously set value (i.e. to remove the value for the property).