Fix case-sensitivity of region-based database observation

[groue]

SQLite is not a case-sensitive database. A table named Player can be named player or PLAYER in SQL requests, without any consequence.

GRDB database observation features ought to support this behavior. When your app observes a request on player, Player or PLAYER, it should be notified of changes applied to player, Player or PLAYER, regardless of the actual name of the database table (player, Player or... PLAYER, yes).

#954 has revealed it was not the case.

When the database table had a name (Player) that did not exactly match the databaseTableName of a record type (player), and you observe Player.fetchCount(db), then all stars would get aligned and trigger a bug:

• The SELECT COUNT(*) FROM player is one of the rare SQL requests that SQLite does not expose to Compile-Time Authorization Callbacks in a regular way. The authorizer is not given the canonical table name used in the schema (Player), but the raw name used in the SQL request: player.
• Thus GRDB would track player.
• And it would miss all subsequent changes performed on Player.

#954 has revealed another bug, with unclear consequences, in the union of database region (see #954 (comment)).

This pull request fixes both bugs by making DatabaseRegion fully case-insensitive.