fix: overwritten backbutton not firing on first time by hardware button and never on back gesture

[GitToTheHub]

Platforms affected

Android

Motivation and Context

• When pressing the back button after the app starts nothing happens. When navigating to another page, the back button js event starts to fire.
• On Android versions, which support the back gesture, nothing happens
• This was due to the empty OnBackPressedCallback.handleOnBackPressed method, which has to forward its call to the WebView, which is done now by a synthetic back button event. If the WebView does not handle the synthetic back button event, the back button if forwarded to cordova.getActivity().getOnBackPressedDispatcher().onBackPressed().
• Generated-By: GPT-5.4, GitHub Copilot Chat

Code cleanup

• Put log warning about back button override on the right place
• resolve methods registerBackPressedCallback and unregisterBackPressedCallback. The code moved to inline code.

Description

Testing

• Tested back button after first start on Android 9
• Test back button gesture on Android 14 and 16

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.43%. Comparing base (1f70d39) to head (9733d15).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1910   +/-   ##
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  Coverage   61.43%   61.43%           
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  Files          24       24           
  Lines        4922     4922           
=======================================
  Hits         3024     3024           
  Misses       1898     1898           

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[Copilot]

Pull request overview

Fixes Android back handling when the Cordova back button is overridden, ensuring the JS backbutton event fires immediately after startup and also when back is triggered via the Android back gesture (OnBackPressedDispatcher path).

Changes:

• Implemented OnBackPressedCallback.handleOnBackPressed() to actively dispatch a synthetic BACK key (DOWN+UP) through the Cordova WebView so existing key routing can fire the JS backbutton event.
• Added fallback to OnBackPressedDispatcher.onBackPressed() when the WebView does not consume the synthetic key events, with temporary callback disabling to prevent recursion.

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[GitToTheHub]

Hi @breautek, what are your thoughts about this PR? Is this ready to merge?

[GitToTheHub]

I made some code cleanup

[breautek]

I don't have any beefs code wise. I'm trusting community feedback on functionality.