qapi: create QAPISchemaDefinition

qapi: create QAPISchemaDefinition

Include entities don't have names, but we generally expect "entities" to
have names. Reclassify all entities with names as *definitions*, leaving
the nameless include entities as QAPISchemaEntity instances.

This is primarily to help simplify typing around expectations of what
callers expect for properties of an "entity".

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240315152301.3621858-6-armbru@redhat.com>