[predictive-back-navigation] replace back handler for ScreenActivity

[lunaticare]

[predictive-back-navigation] replace back handler for ScreenActivity

Summary:

Test Plan:

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Stack created with Sapling. Best reviewed with ReviewStack.

• [predictive-back-navigation] enable for the whole app #773
• [predictive-back-navigation] disable callback when not needed #772
• [predictive-back-navigation] remove deprecated method calls in activities #771
• -> [predictive-back-navigation] replace back handler for ScreenActivity #770
• Make Gradlew executable #769

[what-the-diff]

PR Summary

• Enhances Application Navigation
  Incorporation of OnBackPressedCallback to ScreenActivity.kt provides an efficient way to customize the back navigation behavior across different screens.

• Streamlines Back Navigation Handling
  Implementation of a new method setUpBackHandler() in ScreenActivity.kt reinforces a structured way of managing back navigation events.

• Improves Existing Navigation Method
  Adaptation of onBackPressed() function in ScreenActivity.kt to use OnBackPressedCallback creates a more flexible avenue for handling back press events.

• Optimizes Toolbar Utilization
  Update to onToolbarCreated() method in ScreenActivity.kt to use onBackPressedDispatcher leads to consistent behavior across various toolbar instances.

• Amends Script Execution Permissions
  Modification of the gradlew mode from 100644 to 100755 ensures appropriate execution permissions are set, enhancing system security and performance.