Add Formatter::join

Test: pass
Test: hidl_test
Bug: 32559427
Change-Id: I44e27ba9b2e0fef605c340ba0f70f40ef0e6f390
diff --git a/Method.h b/Method.h
index 229f042..5760d80 100644
--- a/Method.h
+++ b/Method.h
@@ -82,9 +82,10 @@
                               const std::string &className = "",
                               bool specifyNamespaces = true) const;
 
-    static std::string GetArgSignature(const std::vector<TypedVar *> &args,
-                                       bool specifyNamespaces);
-    static std::string GetJavaArgSignature(const std::vector<TypedVar *> &args);
+    void emitCppArgSignature(Formatter &out, bool specifyNamespaces) const;
+    void emitCppResultSignature(Formatter &out, bool specifyNamespaces) const;
+    void emitJavaArgSignature(Formatter &out) const;
+    void emitJavaResultSignature(Formatter &out) const;
 
     const TypedVar* canElideCallback() const;