releasetools: squash backuptool support

This is a squash of the following commits:

Author: Chris Soyars <ctso@ctso.me>
Date:   Thu Dec 23 00:44:33 2010 +0100
    Add otapackage support for backuptool

    Change-Id: I512554c579d444067cd3ccbb0e6946a5eb6bc964a

    Modular backuptool.sh.  Executes backup and restore methods defined in arbitrary /system/addon.d/*.sh scripts.

    * Copy backuptool.functions alongside backuptool.sh.
    * Delete both from /system/bin as they are not useful there.

    Patch Series
    ============
    http://review.cyanogenmod.com/#change,13265
    CyanogenMod/android_build
      * edify generator
    http://review.cyanogenmod.com/#change,13266
    CyanogenMod/android_system_core
      * permissions on /system/addon.d
    http://review.cyanogenmod.com/#change,13267


    CyanogenMod/android_vendor_cm
      * 50-cm.sh reference backup script
      * modular backuptool.sh
      * support backuptool.functions used by /system/addon.d/*.sh scripts

    Change-Id: I26b4907d28f49c69627699d2accd2f0fa2d1b112

    update ota_from_target_files to handle mounting/unmounting for backupscript

    backupscript should not be mounting/unmounting itself as it makes other
    scripts have unexpected results (such as modelid_cfg, which expects /system
    to be mounted)

    instead have the ota script handle the mounting/unmounting

    Change-Id: I94511f4147c624d975cb3ecbeaa8b0e98f63437c

    build: Don't run backuptool on GMS builds

    Change-Id: I5dde27f9d16b88049171db9805221d92e67f3e5d

Author: Tom Marshall <tdm@cyngn.com>
Date:   Wed Apr 9 16:14:07 2014 -0700
    build: edify: use set_metadata for backuptool

    Also use saner permissions on backuptool.sh

    Change-Id: I50742b51867aa358f5924b8dc208833092a35bd9

Author: Ricardo Cerqueira <ricardo@cyngn.com>
Date:   Wed Nov 5 18:16:43 2014 +0000
    ota: Include copies of the recovery scripts even if shipping in block mode

Author: Ricardo Cerqueira <ricardo@cyngn.com>
Date:   Wed Nov 5 19:58:59 2014 +0000
    ota: Fix recovery-script cleanups in block mode

    Change-Id: Iadb480f8062cfb7a0e6c9024e32ac0d71a7481d7

Author: Arian <arian.kulmer@web.de>
Date:   Wed Jun 17 12:35:16 2020 +0200
    build: Disable backuptool on user instead of GMS builds

    * Backuptool is not exclusively used for GApps but
      also used by other things (i.e. Magisk), hence
      it shouldn't be disabled on all GMS builds.

    Change-Id: Ia95c6fed21d7bed5e2e0610aa94264edc1d02c80

Author: Davide Garberi <dade.garberi@gmail.com>
Date:   Tue Sep 24 18:45:17 2019 +0200
    releasetools: Move system mount handling to backuptool

    * This allows the ROM to be flashed on any recovery, whether it mounts
      system to /system, /system_root or /mnt/system like Q recovery

    * Remove any type of system mount with static paths from updater-script
      to figure out the path dinamically through backuptool

    Change-Id: I7b33726305cb6f3eec146d26135f0081002a25dc

Author: Jesse Chan <jc@lineageos.org>
Date:   Fri Jun 12 21:53:18 2020 +0800
    releasetools: support dynamic partitions for backuptool

    Change-Id: I4a04e52f64e307a9852d786aabf17975a020b4b8
Signed-off-by: Jesse Chan <jc@lineageos.org>

Author: Jesse Chan <jc@lineageos.org>
Date:   Tue Jul 7 23:50:10 2020 +0800

    backuptool: do not unmap dynamic partition after finished

    Keep partitions mapped so users can install addons.

    Change-Id: Ic70621986bf136775e686dc8cc690ce076485907
Signed-off-by: Jesse Chan <jc@lineageos.org>

Author: Alessandro Astone <ales.astone@gmail.com>
Date:   Mon Apr 12 18:40:10 2021 +0200

    backuptool: Map extra dynamic partitions for Addon.d V3

    Change-Id: Ia8fa1963c722c5aa2987b947e4e919e19909a9a8

Change-Id: I2401d334d8e16d18d3770b339ec2c787dd8e477c