qapi: provide a friendly string representation of QAPI classes

qapi: provide a friendly string representation of QAPI classes

If printing a QAPI schema object for debugging we get the classname and
a hex value for the instance:

  <qapi.schema.QAPISchemaEnumType object at 0x7f0ab4c2dad0>
  <qapi.schema.QAPISchemaObjectType object at 0x7f0ab4c2dd90>
  <qapi.schema.QAPISchemaArrayType object at 0x7f0ab4c2df90>

With this change we instead get the classname and the human friendly
name of the QAPI type instance:

  <QAPISchemaEnumType:CpuS390State at 0x7f0ab4c2dad0>
  <QAPISchemaObjectType:CpuInfoS390 at 0x7f0ab4c2dd90>
  <QAPISchemaArrayType:CpuInfoFastList at 0x7f0ab4c2df90>

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20231018120500.2028642-1-berrange@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Conditional swapped to avoid negation]
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
[Tweaked to mollify pylint]
Signed-off-by: Markus Armbruster <armbru@redhat.com>