Puts parceled Notif RankingMap in SharedMemory

Puts the RankingMap in a NotificationRankingUpdate in
SharedMemory when it's parceled, and reads it from SharedMemory
when unparceled. This should have the effect of making
NotificationRankingUpdate much smaller to send across Binder.

Also adds Unit Test Coverage for NotificationRankingUpdate.

Bug: 249848655
Test: atest NotificationRankingUpdateTest. Also used
NotificationShellCmd to test issuing 500+ notifications, and observed
reranking occur properly without previously observed binder transaction
failures
Change-Id: I98ebb81905e1c6a0e5e0d7bca9ac715a94e7c7b4

Change-Id: Ied726dae2179cb2f794f166349ee0e9a3e6a2b0d