* Add unit test
* Make sure TextKit components can calculate size in background without upsetting Main Thread Checker
- Add a new thread-safe text view bounds.
- Temporary components stack doesn't have a text view so it can be safely deallocated off main.
* Add ASTextKitComponentsTextView
* Remove unnecessary change
* Fix minor mistake
* ASTextKitComponentsTextView has only 1 initializer
* Minor change
* Switch to atomic property
* Remove manual synthesization
