Support `rows_where()`, `delete_where()` etc for attached alias databases

Hi,

I noticed rows_where() doesn't return any rows from tables which are from attached databases. The exists() function returns false. As far as I can see this is because the table_names() function only looks for table names in the current database and not in attached (or temp) databases.

Besides, rows_where(), also insert_all() and delete_where() didn't do what I was expecting because of this. For the moment I've patched table_names() for myself, see below but I'm not sure what the total impact is on the other functions like lookup truncate etc which all use exists(). Also view_names() doesn't look for views in attached or temp databases.

 def table_names(self, fts4: bool = False, fts5: bool = False) -> List[str]:
        "A list of string table names in this database."
        where = ["type = 'table'"]
        if fts4:
            where.append("sql like '%USING FTS4%'")
        if fts5:
            where.append("sql like '%USING FTS5%'")
        dbs = [x[1] for x in self.execute('pragma database_list').fetchall()]    
        lst=[]
        for db in dbs:    
            sql = "select name from {} where {}".format(db+".sqlite_master"," AND ".join(where))
            lst.extend(r[0] for r in self.execute(sql).fetchall())
        return lst

Start by reading the implementations of table_names(), view_names(), exists(), rows_where(), insert_all(), and delete_where(). Trace how attached and temporary databases are discovered and how those helpers depend on the name lookups. Done means these operations correctly find and act on tables and views across the relevant databases, including the existing FTS filters.