feat: ReVanced Manager as a privileged system app

[0xIO32]

Feature description

Add an alternative installation method to the "Mount install" without requireing root. The ReVanced Manager gets installed as privileged system app and can be included in an aosp build.

Motivation

That way, you have all the benefits of the "Mount install" without having root installed.

Root weakens the security of the device. It should never be possible, that any binary/application on the data partition could gain root permissions. The data partition is read-writable and will not be checked by android verified boot. An attacker can then a: modify an application that has root permissions b (in the example of Magisk, the most popular root solution): modify the magisk database (with the allowed root apps/shells) or just add a script to one of the folders that get executed with root on boot (like service.d or post-fs-data.d or modify a system component directly)

Acknowledgements

• [x] I have checked all open and closed feature requests and this is not a duplicate.
• [x] I have chosen an appropriate title.
• [x] The feature request is only related to ReVanced Manager.