CWG3080 Clarify kinds of permitted template template arguments

Author: eisenwave

source/templates.tex

@@ -1465,11 +1465,14 @@
 template parameter
 shall be the name of a template.
 For a \grammarterm{type-tt-parameter},
-the name shall denote a class template or alias template.
+the name shall denote a class template, alias template, or
+type template template parameter.
 For a \grammarterm{variable-tt-parameter},
-the name shall denote a variable template.
+the name shall denote a variable template or
+variable template template parameter.
 For a \grammarterm{concept-tt-parameter},
-the name shall denote a concept.
+the name shall denote a concept or
+concept template parameter.
 Only primary templates are considered when matching the template template
 argument with the corresponding parameter; partial specializations are not
 considered even if their parameter lists match that of the template template