xs:complexContent with extension results in unusable recursive type

[sirlensalot]

See StrongAccent:
https://github.com/sirlensalot/fadno-xml/blob/master/src/Fadno/MusicXml/MusicXml31.hs#L11152

fadno-xml/xsd/musicxml.30.xsd

Lines 4453 to 4462 in ee456e4

	<xs:complexType name="strong-accent">
	<xs:annotation>
	<xs:documentation>The strong-accent type indicates a vertical accent mark. The type attribute indicates if the point of the accent is down or up.</xs:documentation>
	</xs:annotation>
	<xs:complexContent>
	<xs:extension base="empty-placement">
	<xs:attribute name="type" type="up-down" default="up"/>
	</xs:extension>
	</xs:complexContent>
	</xs:complexType>

Also affects HeelToe, MetronomeTuplet. Note that xs:basicContent with similar application is handled correctly.