C++: Move StdBasicStringStream to a more logical location.

Author: geoffw0

cpp/ql/src/semmle/code/cpp/models/implementations/StdString.qll

@@ -252,13 +252,6 @@ private class StdStringSubstr extends TaintFunction {
   }
 }
 
-/**
- * The `std::basic_stringstream` template class instantiations.
- */
-private class StdBasicStringStream extends ClassTemplateInstantiation {
-  StdBasicStringStream() { this.hasQualifiedName(["std", "bsl"], "basic_stringstream") }
-}
-
 /**
  * The `std::string` functions `at` and `operator[]`.
  */
@@ -563,6 +556,13 @@ private class StdOStreamOutNonMember extends DataFlowFunction, TaintFunction {
   }
 }
 
+/**
+ * The `std::basic_stringstream` template class instantiations.
+ */
+private class StdBasicStringStream extends ClassTemplateInstantiation {
+  StdBasicStringStream() { this.hasQualifiedName(["std", "bsl"], "basic_stringstream") }
+}
+
 /**
  * Additional model for `std::stringstream` constructors that take a string
  * input parameter.