Add batched createAppData API to installd.

Benchmarking creation of new users shows on a freshly setup device
sees many individual binder calls from system server into installd to
create app data directories. Batching these calls shows a significant
performance improvement.

Bug: 153171028
Test: Manually create guest user, trace performance with Perfetto.

Change-Id: Iea43c058d465be44c0937bf6c353555869fc9fd2