Implement BlobStoreManagerService.

This change implements the following APIs with a few TODOs:
- BlobStoreManager.{create,open,delete}Sesison()
- BlobStoreManager.Session.{openWrite,openRead,close,abandon}()
- BlobStoreManager.Session.allow*Access()
- BlobStoreManager.Session.commit()
- BlobStoreManager.openBlob()
- BlobStoreManager.{acquire,release}Lease()

Bug: 143559646
Test: atest cts/tests/BlobStore/src/com/android/cts/blob/BlobStoreManagerTest.java
Change-Id: Id4eb8269f013b5c0ffca63c8251a2553e818091d