SyncManager: Dump per-source last sync time too.

Example:

Per Adapter History
     :
  mak...@gmail.com/com.google u0 [com.google.android.gms.people]
    Per source last syncs:
         OTHER  Success: 2018-04-16 17:03:38  Failure: 2018-04-16 17:04:27
         LOCAL  Success: N/A  Failure: N/A
          POLL  Success: N/A  Failure: N/A
          USER  Success: N/A  Failure: N/A
      PERIODIC  Success: N/A  Failure: N/A
          FEED  Success: N/A  Failure: N/A
    Last syncs:
      2018-04-16 17:04:27 io-error Source=OTHER Elapsed=0s Reason=AutoSync Extras=[]
      2018-04-16 17:03:38 success Source=OTHER Elapsed=5s Reason=AutoSync Extras=[]
      2018-04-16 17:03:20 success Source=OTHER Elapsed=3s Reason=AutoSync Extras=[]

Bug: 76035392
Change-Id: Id73cb10636897c4fe45caad5df13dca8b75381bd
Fixes: 76035392
Test: Manual test with dumpsys content with triggering various syncs