Fix issue where hotseat apps don't migrate to the new grid

Hotseat apps would not migrate to a new grid if the new grid already had
hosteat filled out. This resolves the issue and addresses the issue of
workspace spots showing up as occuppied when they should be available

Bug: 395786587
Test: GridSizeMigrationTest, GridMigrationTest, ValidGridMigrationTest
Flag: EXEMPT bugfix
Change-Id: I79613986702c7dddf15a9a31c29b4ef59eac2b3a