Fixup mounting system on Lineage Recovery

* Lineage Recovery 17.1, like AOSP Q recovery, has '/' as a shared
   mount point, causing `mount --move` to fail.
   If it fails, directly mount system to /system_root via
   /dev/block/ symlinks, like AnyKernel and OpenGapps

Co-authored-by: John Wu <topjohnwu@gmail.com>

scripts/util_functions.sh

@@ -217,7 +217,11 @@ mount_partitions() {
   if [ -f /system/init.rc ]; then
     SYSTEM_ROOT=true
     setup_mntpoint /system_root
-    mount --move /system /system_root
+    if ! mount --move /system /system_root; then
+      umount /system
+      umount -l /system 2>/dev/null
+      mount_ro_ensure "system$SLOT app$SLOT" /system_root
+    fi
     mount -o bind /system_root/system /system
   else
     grep ' / ' /proc/mounts | grep -qv 'rootfs' || grep -q ' /system_root ' /proc/mounts \