Add a copy of AB OTA partition list prop in vendor partition

The sysprop to enable/disable AB OTA update is in vendor partition,
but the sysprop which stores list of AB partitions is in product(which
is on system side of treble boundary). This is inconsistent and might
cause problems during mixed build. To mitigate, add a copy of AB
partition list prop in vendor, and readers of this prop will prefer the
vendor copy instead.

Bug: 283042235
Test: th
Change-Id: Idd73971817f663b08824e285d840ed8d8dd60d2c