[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/struct_test

@@ -0,0 +1,11 @@
+struct Vec2 {
+  x:float;
+  y:float;
+}
+
+table Object {
+  position:Vec2;
+  id:int;
+}
+
+root_type Object;