Spa type refactoring

• Use a more complete API to introspect SPA types
• Avoid the need for the Tables enumeration; the tables are now registered with a string
• Avoid the need for initialization, work directly on spa_types and other static data
• Allow working with Object pods that are not Params; the PARAMS table was previously hardcoded in the pod implementation
• Add a different dynamic type registration system, closer to how spa type works. The only regression is that we can no longer register additional custom object fields (custom SPA_PROP_* for example), but this feature can be re-added later