Add hotseat icons to TestWorkspaceBuilder and submit everything in a batch

Now TestWorkspaceBuilder has the logic to add hotseat icons and
the operations to add items to the Workspace is done in batches
which is faster and more stable. To submit everything in batches
it uses the FavoriteItemsTransaction.

This improves the design because TestWorkspaceBuilder and
HomeScreenImageTest belong to the Test layer and they should
only deal with the logic to run a test and TestWorkspaceBuilder
is the Model layer and holds all the logic to interact with the
Launcher model/data, so this separates the concern of each class.

Also, chagned the name from CellLayoutBoardBuilder to
TestWorkspaceBuilder to make it clearer.

Bug: 243440737
Bug: 235518637
Bug: 242323136
Test: atest HomeScreenImageTest
Test: atest ReorderWidgets
Change-Id: I14eef064fade153b8362537743b061958bb3071d