AppManager as PackageInstaller Frontend Replacement

[Tharow]

While this is nowhere near done the code sections are working,
Discussion about features, documentation, and assoc, is required hence the pull request being opened
Related Issue: #1404

TODO:

• App Archiving/Unarchiving Support for later versions of android.
• Further Integration of session install, and testing
• Use PACKAGE_VERIFICATION_AGENT permission to show current install session that was sent to us and allow modification of session.

Topics/Decisions that need to be made:

• Should AM use PACKAGE_VERIFICATION_AGENT permission at all as it isn't strictly required to function. (See Second TODO for more info)
• Should AM Intercept All Installs? AM will be a Verification Agent with the system allowing it to intercept all installs including any stores with INSTALL_PACKAGES permissions (google play, Galaxy Store, etc)
• Required Documentation for a user to setup AM different configurations:
  • Installation on a re-mountable system image. Including which files need to be transferred.
  • Installation into AOSP/LineageOS build system, Recommended Method
  • Note about building with android.uid.system as shared user id. and Recommendations about SELinux configurations assoc
• Where should required xml config files be stored; listed by folder they go in:
  • default-permissions Not Required grants AM runtime permissions during provisioning step without the user action (user can later deny these permissions)
  • sysconfig Not Strictly Required but Recommended adds AM to hidden-api allow list, backup transport, and allow in power save.
  • permissions Required SystemServer will crash without it. contains privileged permission list, doesn't include signature only permissions
• Should A Magisk systemless package be made for AM (requires testing) and assoc documentation.

[Tharow]

@MuntashirAkon how can i get PackageInstallerActivity to read from an existing session?