Remove support for tuples returned from DatabaseIntrospection.get_field_type().

[Nick Pope]

Following on from #30115, there are two places where DatabaseIntrospection.get_field_type() returns a tuple pair of the string name of the field type and a dictionary of extra parameters for the field type:

1. For the SQLite backend where a field has a size, e.g. varchar(40).
2. For the PostGIS backend where we need to handle geography data types.

The SQLite case led to an obscure bug that has been addressed for #30115 by removing it as it turned out that the max_length value was already handled.

This leaves only the PostGIS case which this ticket proposes to replace with an alternative solution, as well as the removal of workarounds in the test suite that handle tuples returned from DatabaseIntrospection.get_field_type().

[Nick Pope]

​PR

Marked as accepted based on comments in original ​PR from which this is derived.

[Tim Graham <timograham@…>]

In 327bbaa:

Refs #30123 -- Changed second arg of DatabaseIntrospection.get_geometry_type() to the row description.

[Tim Graham <timograham@…>]

In 8d01edf:

Refs #30123 -- Simplified introspection of geography columns on PostGIS.

[Tim Graham <timograham@…>]

In 0ef99796:

Fixed #30123 -- Removed tuple support in DatabaseIntrospection.get_field_type().

Support for returning tuples was undocumented and error prone.