Support updateable groups.

Adds updateable group support to OTA.

* DeltaPerformer combines partition sizes with
  dynamic_partition_metadata to
  BootControlInterface::PartitionMetadata.

* BootControlAndroid::InitPartitionMetadata:
    * Copy all groups / partitions from source metadata slot
    * Remove all groups / partitions mentioned in the manifest (of the
    target slot)
    * Re-add all groups / partitions mentioned in the manifest.

* BootControlAndroid::InitPartitionMetadata can check
  the incoming PartitionMetadata to see if a partition is dynamic
  or not. The guessing logic is completely removed.

* Because a partition is removed then re-added, there is no need
  for preserving the entry with size 0 to indicate that a partition
  is removed. When update_engine sees a partition in a group "foo" on
  the device, but manifest contains group "foo" without the partition,
  it removes the partition.

* Hence, Removing a partition does NOT require keeping the entry (i.e.
  RemovePartition is used instead of ShrinkPartition(0) ). This makes
  retrofitting dynamic partitions on older devices easier.

The following is now allowed:
- Adding / removing / resizing partitions
- Adding / resizing groups

It is not allowed to remove a group, but a group can always be resized
to zero to deprecate it.

Test: update_engine_unittests
Bug: 117182932

Change-Id: I39d77f1d1d1fc52fc245f3de699635e6a429015e