Currently child options are applied only for visible children. During push animations, both children are visible.
If mergeOptions is called on the disappearing child during push animation, wrong options will be applied.

This commit changes the conditional so that child options are merged to stack if the child is also the current child.

This adds an Android-only flag blurOnUnmount, that if true when calling push, pop, showModal, dismisModal, as well as when true on the component's static options(passProps) { ... } return value, will cause RNN to check for any focused views when the component the flag was passed for is being unmounted, and blur said view if it exists, causing not just the view to lose focus, but also the soft keyboard to be dismissed.

We added this to our fork of RNN to tackle issues stemming from an inability to dismiss the soft keyboard on unmounting components, due to the disappear/unmount lifecycle events of the component coming too late for our keyboard dismissal calls to make it across the native<->js bridge before the component was unmounted.

As this functionality is hidden behind a flag and does not alter base functionality, and the issue it seeks to solve might have been encountered by other users of RNN, I figured I might as well submit a PR to see if there is interest in merging this back into the base.

Currently options are applied when a view is visible. This caused some noticeable flickering when
switching to tabs for the first time.
This commit adds a new callback which ViewController can override - onAttachToParent.
StackController now uses it to apply options which prevents flickering.

* Apply modalPresentationStyle and modalTransitionStyle on childWillMoveToParent

* Fixes unit tests

* Fixes flaky unit tests caused by OCMock

Fixes #4138

* Handle pop and dismissModal rejections - #3914

* Added e2e

* Update TextScreen.js

Added unit test coverage on iOS

Options were merged after screen was popped from the backing stack data structure.
This meant that options were not resolved correctly for it as it was already detached from the stack.
This was especially noticeable when declaring a custom animation is mergeOptions passed to Navigation.pop().

Fixes #3869 and closes #4138

In some places “enable” was used to control certain options. This commit adds backwards compatible support
for “enabled” property which should be used from now on.

Overflow button color is based of `options.topBar.rightButtonColor`, this might change in the future.

This commit adds a dedicated RN 57 build flavour for the Wix fork, where 506f920838 is reverted.
The revert reintroduced UiImplementationProvider which is required to pass SyncUiImplementation to UiManager.