tame: rater.xsd: templateName: Permit multiple leading/trailing underscores

This is needed by TAMER's template desugaring.  The XSD is superceded by
`nir::parse`, but can't go away until TAMER fully supplants the XSLT-based
compiler.

...and after all this time, I still never got rid of the duplicate XSD.  Or
even recall which one is the duplicate.

DEV-13708

rater/rater.xsd

@@ -150,7 +150,7 @@
     </xs:annotation>
 
     <xs:restriction base="xs:string">
-      <xs:pattern value="_[a-zA-Z0-9@\{\}-]+_|@[a-z][a-zA-Z0-9]*@" />
+      <xs:pattern value="_+[a-zA-Z0-9@\{\}-]+_+|@[a-z][a-zA-Z0-9]*@" />
     </xs:restriction>
   </xs:simpleType>
 

src/current/rater.xsd

@@ -148,7 +148,7 @@
     </xs:annotation>
 
     <xs:restriction base="xs:string">
-      <xs:pattern value="_[a-zA-Z0-9@\{\}-]+_|@[a-z][a-zA-Z0-9]*@" />
+      <xs:pattern value="_+[a-zA-Z0-9@\{\}-]+_+|@[a-z][a-zA-Z0-9]*@" />
     </xs:restriction>
   </xs:simpleType>