fix(ios): Reset plugin listeners when WebView process is terminated

[gabeschine]

Fixes #7810

This fixes an issue where, after the native WebView process is terminated, some messages from Native -> JS fail to be delivered to the JS side. In our production app, the important messages were appUrlOpen from the @capacitor/app plugin, and pushNotificationReceived from @capacitor/push-notifications.

The issue seems to have been present because the Capacitor plugins held onto stale listener registrations - with no counterpart in JS after a WebView kill - which made them send messages immediately (despite retainUntilConsumed being set to true) instead of waiting for a first listener.

Testing

• Successfully passes tests in the minimal reproduction app / test suite: https://github.com/watch-duty/capacitor-message-bug-repro
• Patched into our production app on top of Capacitor v6.1.2, no concerns raised, deeplinks work as expected

Test runs from above test suite

NOTE: ! denotes an inconclusive run

Before:

FF!FF!!FF!

After:

!!........

[markemer]

This is a nice find.