RUMM-1758 Fix 'Library not loaded: SwiftUI' runtime crash in nightly tests (iOS 11 and 12)

[ncreated]

What and why?

🐞⚙️ This PR fixes the runtime issue appearing in nightly tests for iOS 11 and 12:

dyld: Library not loaded: /System/Library/Frameworks/SwiftUI.framework/SwiftUI
  Referenced from: /Users/vagrant/Library/Developer/CoreSimulator/Devices/7795F4B9-88DD-4620-B70C-CECE75CF3516/data/Containers/Bundle/Application/F5F467F7-4D89-4EB2-9504-0773865DB814/Example.app/Example
  Reason: image not found

How?

The issue was introduced in #669, where SwiftUI code was added to Example app. The solution is to add a weak reference to SwiftUI.framework in this target:

Review checklist

- [] Feature or bugfix MUST have appropriate tests (unit, integration)

• Make sure each commit and the PR mention the Issue number or JIRA reference