`navigate`

BREAKING CHANGE: Previously, `navigate` method navigated back if the screen
already exists in the stack. I have seen many people get confused by this
behavior. This behavior is also used for sending params to a previous
screen in the documentation. However, it's also problematic since it could
either push or pop the screens based on the scenario.

This removes the going back behavior from `navigate` and adds a new method
`popTo` to go back to a specific screen in the stack.

The methods now behave as follows:

- `navigate(screenName)` will stay on the current screen if the screen is
already focused, otherwise push a new screen to the stack.
- `popTo(screenName)` will go back to the screen if it exists in the stack,
otherwise pop the current screen and add this screen to the stack.
- To achieve the previous behavior with `navigate`, you can use the `getId`
prop in which case it'll go to the screen with the matching ID and push or
pop screens accordingly.

BREAKING CHANGE: Previously, the `onReady` prop and `navigationRef.isReady()` work slightly
differently. The
`onReady` callback fired when `NavigationContainer` finishes mounting and deep links is resolved.
The `navigationRef.isReady()` method additionally checks if there are any navigators rendered - which may not be `true` if the user is rendering their navigators conditionally inside a
`NavigationContainer`.

This changes `onReady` to work similar to `navigationRef.isReady()`. The `onReady` callback will now fire only when there are navigators rendered - reflecting the value of
`navigationRef.isReady()`.

PR removes deprecation warnings introduced in react-navigation@8e0ae5f

…t-navigation#10905)

Due to backward compatibility reasons, React Navigation 5 and 6 support navigating to a screen in a child navigator with `navigation.navigate(ScreenName)` syntax. But this is problematic with the new architecture - it only works if the navigator is already mounted, doesn't work with TypeScript, etc. That's why there's a special API to navigate to a nested screen (`navigation.navigate(ParentScreenName, { screen: ScreenName })`).

This drops this behavior and adds a prop to explicitly enable it to make it easier to migrate. This prop will be removed in the next major.