feat(core): back button event on Android, closes #8142

[tomerqodo]

Benchmark PR from qodo-benchmark#30

[sentry]

Bug: The logic in the Android back button handler is inverted. It performs default navigation when a listener is registered and tries to trigger an event when no listener exists.
_{Severity: CRITICAL}

Suggested Fix

Invert the conditional logic in the handleOnBackPressed method. The block that calls trigger(BACK_BUTTON_EVENT, data) should be executed when hasListener(BACK_BUTTON_EVENT) is true, and the default navigation logic should be moved to the else block.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: crates/tauri/mobile/android/src/main/java/app/tauri/AppPlugin.kt#L30-L41

Potential issue: The conditional logic in the `handleOnBackPressed` method is inverted.
The code checks `if (hasListener(BACK_BUTTON_EVENT))`, and if true (meaning listeners
are registered), it proceeds to execute the default back navigation behavior instead of
notifying the listeners. Conversely, in the `else` block where no listeners are
registered, it attempts to call `trigger()` to notify listeners, which does nothing.
This effectively breaks the intended functionality of the back button event listener on
Android, as registered listeners will never be called, and the default behavior will not
work when no listener is present.

_{Did we get this right? 👍 / 👎 to inform future reviews.}