InAppBrowser previous content persists after ref.show()

### Issue Type

- [x] Bug Report
- [ ] Feature Request
- [ ] Support Question

## Description
Tried to hide the window on the 'unload' event and show it on the 'loadstop' event. The previous content is shown initially and the new content starts drawing after which makes a flicker. I assume this is not the expected behavior.

### Command or Code
```
ref.addEventListener('loadstop', () => {
ref.executeScript({
code: `
window.addEventListener("beforeunload", function(event) {
webkit.messageHandlers.cordova_iab.postMessage(JSON.stringify({
hide: true,
}))
});
`
});
});
```

Platform: Android 9.0
Cordova: 10.0.0
InAppBrowser: 5.0.0

## Checklist

- [x] I searched for already existing GitHub issues about this
- [x] I updated all Cordova tooling to their most recent version
- [x] I included all the necessary information above

Reproduce the Android 9.0 flow around ref.show(), loadstop, and the beforeunload handler, then trace the InAppBrowser Android implementation responsible for displayed content during navigation. Done means ref.show() no longer briefly displays the previous page before the new content is drawn.

Written by the indexing model from the issue text.