[AstMatcher]templateArgumentCountIs support FunctionDecl

`hasTemplateArgument` and `templateArgumentCountIs` are always used together. It is more convenient to make then support `FunctionDecl`.

Author: HerrCai0907

clang/include/clang/ASTMatchers/ASTMatchers.h

@@ -1090,6 +1090,7 @@ AST_POLYMORPHIC_MATCHER_P2(
 AST_POLYMORPHIC_MATCHER_P(
     templateArgumentCountIs,
     AST_POLYMORPHIC_SUPPORTED_TYPES(ClassTemplateSpecializationDecl,
+                                    VarTemplateSpecializationDecl, FunctionDecl,
                                     TemplateSpecializationType),
     unsigned, N) {
   return internal::getTemplateSpecializationArgs(Node).size() == N;