Make it work with 'UnitOf<Ulid>'

[Funkest]

• UnitOf(typeof(Ulid), ...) works, but UnitOf<Ulid>(...) does not work in lastest version.
• var innerTypeName = prop.TypeName; throws due to props.Type null.
  • In SyntaxReceiver.OnVisitSyntaxNode(), UnitOf<Ulid> appears as not PredefinedTypeSyntax, but IdentifierNameSyntax

[hadashiA]

I tested it and it seems to work well. Thanks a lot !