Refactor database-related code in ApiQueryWatchlistRaw

Refactor database-related code in ApiQueryWatchlistRaw

Database queries used to get user's watchlist items in API are quite
complex due to number of options oferred by the API.
Generating the query is moved to WatchedItemQueryService.
ApiQueryWatchlistRaw no longer contains database-related code.

Simple user watchlist item lookups should use WatchedItemStore.

ApiQueryWatchlistRaw tests have been introduced in
I9c07aa237607143985f0efe20ed0065d2bde27e4

Bug: T132566
Change-Id: I875a92074b52c00ac11db1fa05615abbf5262ab1