Ensure Background sync is not stopped when there is an active call.

[bmarty]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Ensure Background sync is not stopped when there is an active call.
It was happening since the application is foregrounded when VectorCallActivity is displayed.

Motivation and context

Closes #4066

Screenshots / GIFs

Tests

1. Clear task (make sure Element is not running on the background).
2. Turn off/lock the screen.
3. Don't do anything, let the screen wake up by itself from call notification.
4. Don't pick up the call.

Then either the caller cancel the call, or answer the call from another session.

Previously the call was ringing forever. With this change, the device stops ringing, and the background sync is correctly cancelled. The device does not need to sync forever once the call is over.

Also did some smoke test around call, since this code is quite complex and not covered by unit tests.

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/vector-im/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

0.0% Coverage
0.0% Duplication

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[opusforlife2]

Hi, @bmarty. There's no release issue for 1.6.8, so I'm pinging you here. Could you please let the F-Droid team know so that F-Droid users can get this version?