Present contacts picker on main thread

[mourad-brahim]

Platforms affected

iOS

Motivation and Context

Fix crash on iOS 14

Description

Fix crash on iOS 14

Testing

Tested on iPhone/Simulator running iOS 14

Checklist

• [x] I've run the tests to see all new and existing tests pass
• [x] I added automated test coverage as appropriate for this change
• [ ] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [x] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [x] I've updated the documentation if necessary