`main()` function used to be needed to support dart, since dart
Does not allow top level statements. Since we no longer use dart
The need for `main()` has been removed.
In preparation for `Basel` and standardized way of running tests
we are removing `main()`
PR Close#21053
Add testability hook to downgraded component so that protractor can wait for asynchronous call to complete.
Add unregisterApplication() and unregisterAllApplications() to testability registry for cleaning up testability and unit test.