FTS index table not have to be qualified by data source alias in query

For function match(), the first argument refers to the FTS index table. Syntactically, it appears as a property path. The leading part may be the alias of a data source. It is required if there multiple data sources. In Lithium, all data sources must come from the same database table. For Helium, they may refer to multiple tables If the property path representing the FTS table is not prepended with an alias, we should not allow it even if there are multiple data sources as long as there is unique database table involved in the query.