Fix crashes due to wrong root fragment manager

[Stypox]

What is it?

• Bugfix (user facing)
• Feature (user facing)
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

In NewPipe the MainFragment is entitled to handling the fragment backstack and the collapsible player fragment. Therefore any action involving opening new fragments (e.g. when clicking on videos/playlists/...) needs to be performed on the MainFragment's fragment manager. The previous implementation chose the fragment manager assuming that every fragment is at most singly nested (i.e. where the parent is directly MainFragment). However the new main page channel tab contains doubly-nested fragments (i.e. the channel tabs), so the previous method was choosing the wrong fragment manager, making the app crash. This PR fixes the issue by properly finding the root fragment.

Fixes the following issue(s)

• Release v0.26.0 (please TEST!) #10471 (comment)

APK testing

The APK can be found by going to the "Checks" tab below the title. On the left pane, click on "CI", scroll down to "artifacts" and click "app" to download the zip file which contains the debug APK of this PR. You can find more info and a video demonstration on this wiki page.

Due diligence

• I read the contribution guidelines.

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

0.0% Coverage
0.0% Duplication

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