[cling] Fully desugar UsingType in GetFullyQualifiedType

UT->getUnderlyingType() which only strips one sugar layer, stopping at the
first TypedefType rather than reaching the canonical type.

Use QT.getCanonicalType() instead to strip all sugar layers at once.

Author: devajithvs

interpreter/cling/lib/Utils/AST.cpp

@@ -1725,8 +1725,8 @@ namespace utils {
 
     // We don't consider the alias introduced by `using a::X` as a new type.
     // The qualified name is still a::X.
-    if (const auto* UT = QT->getAs<UsingType>()) {
-      QT = Ctx.getQualifiedType(UT->getUnderlyingType(), prefix_qualifiers);
+    if (QT->getAs<UsingType>()) {
+      QT = Ctx.getQualifiedType(QT.getCanonicalType(), prefix_qualifiers);
       return GetFullyQualifiedType(QT, Ctx);
     }
 

roottest/root/meta/naming/execResolveTypedef.cxx

@@ -225,7 +225,7 @@ int execResolveTypedef()
 
    testing("unsigned int", TClassEdit::ResolveTypedef("SG::sgkey_t"));
    testing("unsigned int", TClass::GetClass("PackedParameters")->GetDataMember("m_sgkey")->GetTrueTypeName());
-   testing("uint32_t", TClass::GetClass("PackedParameters")->GetDataMember("m_sgkey")->GetFullTypeName());
+   testing("unsigned int", TClass::GetClass("PackedParameters")->GetDataMember("m_sgkey")->GetFullTypeName());
    testing("RT::EX::ClusterSize", TClassEdit::ResolveTypedef("RT::EX::ClusterSize_t"));
    return 0;
 }