[fuzzer] Adds code generation target. (#8795)

* adds code generation fuzzer target.

* add buffer verification

* add table verification in codegen fuzzer

---------

Co-authored-by: Björn Harrtell <bjornharrtell@users.noreply.github.com>

tests/fuzzer/seed_codegen/rpc_test

@@ -0,0 +1,14 @@
+table Request {
+  id:int;
+  message:string;
+}
+
+table Response {
+  result:string;
+}
+
+rpc_service MyService {
+  DoSomething(Request):Response;
+}
+
+root_type Request;