Panic on converting regclass to string

[zachmu]

Running this query with the DEBUG_ANALYZER=true environment:

SELECT relname FROM pg_catalog.pg_class WHERE oid = 'testing'::regclass;

Yields a panic. The root cause is that the regclass cast expression is having String() called on it, which eventually calls this:

func (t *DoltgresType) FormatValue(val any) (string, error) {
	if val == nil {
		return "", nil
	}
	// TODO: need valid sql.Context
	return t.IoOutput(nil, val)
}

Which ultimately calls:

// regclassout represents the PostgreSQL function of regclass type IO output.
var regclassout = framework.Function1{
	Name:       "regclassout",
	Return:     pgtypes.Cstring,
	Parameters: [1]*pgtypes.DoltgresType{pgtypes.Regclass},
	Strict:     true,
	Callable: func(ctx *sql.Context, _ [2]*pgtypes.DoltgresType, val any) (any, error) {
		// Find all the schemas on the search path. If a schema is on the search path, then it is not included in the
		// output of relation name. If the relation's schema is not on the search path, then it is explicitly included.
		schemasMap, err := settings.GetCurrentSchemasAsMap(ctx)

This is easy to trigger with the debug env vars, but will also happen when running DESCRIBE statements, and probably in other circumstances (column default values, really any time we need to convert a regclass to a string).

Not sure the best fix.