MountSuspended should consider any directives added to the vue app

[joel-wenzel]

Describe the feature

Right now custom directives are not available when running tests. For example I have a custom uppercase directive and when testing the text field component I get:

[Vue warn]: Failed to resolve directive: uppercase
  at <MountSuspendedComponent >
  at <MountSuspendedHelper>
  at <Anonymous ref="VTU_COMPONENT" >
  at <VTUROOT>

Additional information

• Would you be willing to help implement this feature?
• Could this feature be implemented as a module?

Final checks

• Read the contribution guide.
• Check existing discussions and issues.