adb: add overlayfs handling for readonly system filesystems

adb verity-on setup overlayfs directories, do not skip if verity
feature not configured for device.

adb verity-off teardown overlayfs directories, do not skip if verity
feature not configured for device.

adb remount setup overlayfs directories and mount if possible, and
do so without a reboot if possible.

Test: compile
Bug: 109821005
Bug: 110985612
Change-Id: I28c4c23fea44b886c5523f0286a523f0b0485df0