Fix XSD generator to respect required field attribute

modello-plugins/modello-plugin-xsd/src/main/java/org/codehaus/modello/plugin/xsd/XsdGenerator.java

@@ -87,6 +87,8 @@ private void generateXsd(Map<String, Object> parameters) throws IOException, Mod
 
         // we assume parameters not null
         String xsdFileName = (String) parameters.get(ModelloParameterConstants.OUTPUT_XSD_FILE_NAME);
+        // enforceMandatoryElements parameter is kept for backward compatibility but is no longer used.
+        // Required fields are now always enforced based on field.isRequired() value.
         boolean enforceMandatoryElements =
                 Boolean.parseBoolean((String) parameters.get(ModelloParameterConstants.XSD_ENFORCE_MANDATORY_ELEMENTS));
 
@@ -232,9 +234,7 @@ private void writeComplexTypeDescriptor(
                     }
                     w.startElement("xs:element");
 
-                    if (!enforceMandatoryElements || !field.isRequired()) {
-                        // Usually, would only do this if the field is not "required", but due to inheritance, it may be
-                        // present, even if not here, so we need to let it slide
+                    if (!field.isRequired()) {
                         w.addAttribute("minOccurs", "0");
                     }
                 }

src/main/mdo/modello.mdo

@@ -672,7 +672,6 @@
         <field xml.insertParentFieldsUpTo="versionRange">
           <name>type</name>
           <version>1.0.0+</version>
-          <required>true</required>
           <type>String</type>
           <description><![CDATA[
             Simple type for this field (or array of such type). Can be one of : <code>boolean</code>, <code>byte</code>,