Message and MimeMessage were creating a lot of unnecessary sub-objects
even when not needed, so do a bunch of lazy initialization. This should
raise the bar on the size of gigantic inboxes giving us trouble.
* Specific optimizations:
* Replace date formatter with a shared static
* lazy create mHeader (ArrayList)
* lazy create mFlags (HashSet)
* optimize MimeHeader fields class
* lazy create local message-ID (expensive-to-make uuid String)
* make message-id string less expensive to create
* Other cleanups:
* add some override annotations
* privatize some members
* update a fragile test (not a deep fix, it's still fragile)
Side effect, should be faster too.
Bug: 2357564
Bug: 2093422
Change-Id: I8a873879d402e2662339d5398ad0b15da6e580e9
44552da606