Changing IMM#hideSoftInputFromWindow return value for app with target SDK's < B

Some older apps are calling InputMethodManager#hideSoftInputFromWindow multiple times, until it returns false, to show then their in-app keyboard. Before Android Baklava, the return value was an indicator, whether the request has been send to IMMS. For apps targeting those releases, we return true only if the IME was requested visible before.
Apps that target Android Baklava and onwards should use the View.OnApplyWindowInsetsListener to get changes in the IME visibility.

Fix: 395521150
Fix: 395986009
Flag: android.view.inputmethod.refactor_insets_controller
Test: manual with app with targetSDK < Android Baklava: call IMS#hideSoftInputFromWindow while IME is showing (expect true), and while hidden (expect false)
Change-Id: I1e4588f017fecd49b3aa999fa7749ae7a3bb0d1e