Change grid migration to start from top to bottom

Fix: 222236363
Test: GridSizeMigrationTaskV2Test
Test: 4x4 -> 4x5/5x5 migration, 5x5 -> 4x5/4x4 migration
Change-Id: Id5d87b5d0bf9d7cc9154de81dd5edfb0ca9fa633
2 files changed