Reland: "init: chroot from recovery to /first_stage_ramdisk"

When using the recovery image as a trampoline to boot the system,
first chroot from the recovery image to /first_stage_ramdisk, to
minimize differences between these two boot paths.

Primary motivation is due to the fact that the basename of each mount
point is used by device-manager to name its nodes, and the previous
code that created used /system_recovery_mount as the mount point for
system.img broke AVB.  Instead of hacking around that issue, this
change unified mounting for the recovery trampoline and true first
stage ramdisk paths.

Change when relanding: the original change skipped the move mount from
/first_stage_ramdisk to / and only did a chroot instead.  This was a
mistake that resulted in the subsequent move mount of /system to / to
mount over the '/' directory instead of moving that mount.  This
change uses a bind mount of /first_stage_ramdisk to itself instead of
skipping the first move mount.

Bug: 114062208
Test: AVB works with blueline_mainline
Change-Id: I65207edfe98531892da2eafcbff19b438c9c64fe