MOBILEWEBVIEW-126: change back action handler

[sergeysozinov]

https://tracker.yandex.ru/MOBILE-38

[Copilot]

Pull request overview

Updates in-app back navigation handling by replacing OnBackPressedCallback usage with a custom back-press registration mechanism that combines layout key-event interception and Android 13+ system back callbacks.

Changes:

• Introduced BackPressRegistrar / BackRegistration abstractions and wired them into MindboxView.
• Added BackButtonLayout + BackButtonHandler and implemented them in InAppConstraintLayout to intercept BACK key events.
• Updated WebView and Modal in-app view holders to bind back actions via AbstractInAppViewHolder.bindBackAction.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/WebViewInappViewHolder.kt	Switches WebView in-app back handling to bindBackAction (removes OnBackPressedCallback).
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/ModalWindowInAppViewHolder.kt	Switches modal in-app back handling to bindBackAction (removes OnBackPressedCallback).
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/InAppConstraintLayout.kt	Adds BACK key interception and supports BackButtonLayout.
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/BackPressRegistrar.kt	New registrar that wires layout back listener + Android 13+ OnBackInvokedCallback.
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/BackButtonLayout.kt	New interface for layouts that can accept a back listener.
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/BackButtonHandler.kt	New helper to consume only valid BACK/ACTION_UP events.
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/view/AbstractInAppViewHolder.kt	Adds centralized back registration lifecycle management.
sdk/src/main/java/cloud/mindbox/mobile_sdk/inapp/presentation/InAppMessageViewDisplayerImpl.kt	Replaces registerBack API with backPressRegistrar on MindboxView.

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