Add pending system update info system APIs.

This CL adds system APIs in android.os.SystemUpdateManager. The APIs allow
system updater apps (RECOVERY permission required) to publish the pending
system update information, and allow other apps to query the info
accordingly (requiring RECOVERY or READ_SYSTEM_UPDATE_INFO permission).

Design doc in go/pi-ota-platform-api.

Bug: 67437079
Test: Use test apps to call the new APIs to query and set the update info
      respectively.
Change-Id: Id54b4a48d02922d2abd906dd7e2ec80a656fc9b1