Support grid preview with v2 migration algorithm

The focus of ag/10346770 is around the actual algorithm, while in the meantime our preview logic has changed during the code review of ag/10100264.

GridSizeMigrationTaskV2 addresses both cases, the difference being preview passes in constructed IDP while actual migration uses IDP from the current Context.

When doing actual migration, we call METHOD_UPDATE_CURRENT_OPEN_HELPER to update the current db helper and copy the favorites table from the previous db into the current db in favorites_tmp table. Then we do migration from there.

When calculating preview, I added METHOD_PREP_FOR_PREVIEW in this change to copy the favorites table from the intended grid setting to the current grid setting in favorites_preview table. Then we calculate migration from the current favorites table to favorites_preview table and save into favorites_preview table.

Bug: 144052802
Fixes: 144052839

Test: Manual

Change-Id: I64a8b61a4e0bf8399c0ae1af4ef9d2bde0f1ee2f