Create a fetcher for converted legacy list widgets

We create a fetcher in AppWidgetHost dedicated for fetching latest
RemoteViews from the service for converted legacy list widgets since
they usually contain a large number of entries and could potentially
cause TransactionTooLargeException, as a result dropping the host
connection in the widget service and blocking future updates.

Test: N/A
Bug: 245950570
Change-Id: I65d5a675b34adff1db6463e513395207d542f766