Fix: Allow empty text content in height element

Changed base type from xs:decimal to xs:string to support:
- <height value='50.0'/> (attribute only, empty content)
- <height value='50.0'>50.0</height> (both attribute and content)

ATAK uses attribute-only format which was failing validation.

Author: pdfinn

validator/schemas/details/height.xsd

@@ -1,8 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
-  <xs:complexType name="detail_height" mixed="true">
+  <xs:complexType name="detail_height">
     <xs:simpleContent>
-      <xs:extension base="xs:decimal">
+      <xs:extension base="xs:string">
         <xs:attribute name="value" type="xs:decimal"/>
       </xs:extension>
     </xs:simpleContent>