sql/sem/types: more efficiently order UserDefinedTypeMetadata fields

The order of fields of the `types.UserDefinedTypedMetadata` struct,
which is embedded in `types.T`, has been changed to reduce padding
required for word-alignment. The struct size has been reduced from 32
bytes to 24 bytes.

Release note: None

Author: mgartner

pkg/sql/types/types.go

@@ -192,13 +192,13 @@ type UserDefinedTypeMetadata struct {
 	// Name is the resolved name of this type.
 	Name *UserDefinedTypeName
 
+	// EnumData is non-nil iff the metadata is for an ENUM type.
+	EnumData *EnumMetadata
+
 	// Version is the descriptor version of the descriptor used to construct
 	// this version of the type metadata.
 	Version uint32
 
-	// EnumData is non-nil iff the metadata is for an ENUM type.
-	EnumData *EnumMetadata
-
 	// ImplicitRecordType is true if the metadata is for an implicit record type
 	// for a table. Note: this can be deleted if we migrate implicit record types
 	// to ordinary persisted composite types.