fix(browser): only fire browserFinished when the Custom Tab actually terminates

[OS-ruimoreiramendes]

Description

Refactor the Android browser plugin to use ActivityResultLauncher for detecting when the Custom Tab has actually terminated, instead of inferring closure from lifecycle events via the previous EventGroup counter.
The EventGroup helper is removed. Browser now exposes setCustomTabLauncher and BrowserControllerActivity registers a launcher via registerForActivityResult, the browserFinished event is only fired when the launched Custom Tab activity ends.

Fixes #2554.

Change Type

• Fix
• Feature
• Refactor
• Breaking Change
• Documentation
• Other (CI, chores, etc.)

Rationale / Problems Fixed

When the user minimizes the Chrome Custom Tab to Picture-in-Picture (or backgrounds the app), the previous heuristic counted TAB_HIDDEN + unbindService and inferred the tab had closed firing browserFinished even though the tab was still open. After that, subsequent minimize/maximize/close events wouldn't fire the event again.

ActivityResultLauncher provides a single, deterministic callback only when the Custom Tab activity
truly finishes, so browserFinished now reflects the actual closed state.

Tests or Reproductions

Reproduced with the repo:
https://github.com/Prinzhorn/capacitor-android-browser-close-event

Manually tested on a physical Android device:

• Open browser → close via back gesture / X button → browserFinished fires once
• Open browser → minimize to PiP → maximize → close → browserFinished fires once, only on close
• Open browser → send app to background → return to app → close browser → browserFinished fires once,
  only on close

Platforms Affected

• Android
• iOS
• Web