Fixing the hotseat import logic

The import logic following the behavior: Improt everything and force
run GridMigrationTask to automatically remove broken icons.
This logic would fail for hotseat as the replacement happens before
the GridMigrationTask, which will not replace the broken targets
appropriately

The cl changes some logic only for hotseat import
> After import remove any broken icons/empty folders
> When adding default icons, only add as much icons as required. Since
GridMigrationTask uses weights, it sometimes removes imported icon, if
the hotseat size becomes too large.

Bug: 30909630
Change-Id: I6ca1f25dac81649794d81aaf82c3c38d1c918d91