Fix folder sync parsing and parent initialization

* This is a large CL, but almost all of it relates to more
  comprehensive tests for folder parsing
* There are less than a dozen lines of production code changes:
  - Move creation of mailboxMap out of the validation loop in
  - Make sure we fix up the parent of new/changed folders
    in MailboxUtilities

Bug: 5794371

Change-Id: I5fb32369a6fdbfb33919df495d40347b56013bbd
7 files changed