Fix use of CXXThisScopeRAII

Seemingly I managed to not give this a name, and not notice that it
didn't properly introduce the scope it was supposed to!  This patch
gives it a name which should hopefully/presumably fix any cases where we
don't properly introduce the 'this' scope.  I presume that previous
callers to this might also do this in most cases so that this is a
redundant scope, but we have to make sure it happens.

FIXES: #130846

Author: erichkeane

clang/lib/Sema/SemaTemplate.cpp

@@ -5845,7 +5845,7 @@ bool Sema::CheckTemplateArgumentList(
       ThisQuals = Method->getMethodQualifiers();
 
     ContextRAII Context(*this, NewContext);
-    CXXThisScopeRAII(*this, RD, ThisQuals, RD != nullptr);
+    CXXThisScopeRAII Scope(*this, RD, ThisQuals, RD != nullptr);
 
     MultiLevelTemplateArgumentList MLTAL = getTemplateInstantiationArgs(
         Template, NewContext, /*Final=*/false, CTAI.CanonicalConverted,