Foster auto-incremented primary keys

[groue]

This PR introduces the TableDefinition.autoIncrementedPrimaryKey method, that defines an auto-incremented integer primary key. The documentation has been updated in order to foster this method:

try db.create(table: "players") { t in
    // Recommended
    t.autoIncrementedPrimaryKey("id")
    
    // Still valid, but no longer recommended:
    t.column("id", .integer).primaryKey()
    
    ...
}

An auto-incremented primary key comes with the guarantee that ids are never reused. It is safer than an integer primary key that is not auto-incremented, and can reuse ids:

Imagine an application screen that displays and tracks the player with id 1. In the background, the application synchronizes the players with some server content. The player 1 is destroyed. A new and different player is inserted. If the primary key is not auto-incremented, SQLite can reuse the id 1 for the newly inserted player: the application screen may not notice that its player was destroyed, and may display the new player instead: this is a bug.

This kind of dangerous scenario is unfortunately likely to happen with the database observation tools that come with GRDB: FetchedRecordsController and RxGRDB. Even though both track changes in order to fetch fresh request results, they don't care about individual changes, and do not notice id reuses.

This is why we now foster the safest option: auto-incremented primary keys. Expert users can still use naked integer primary keys when they need.