[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/monster_sample

@@ -0,0 +1,33 @@
+// Example IDL file for our monster's schema.
+
+namespace MyGame.Sample;
+
+enum Color:byte { Red = 0, Green, Blue = 2 }
+
+union Equipment { Weapon } // Optionally add more tables.
+
+struct Vec3 {
+  x:float;
+  y:float;
+  z:float;
+}
+
+table Monster {
+  pos:Vec3;
+  mana:short = 150;
+  hp:short = 100;
+  name:string;
+  friendly:bool = false (deprecated);
+  inventory:[ubyte];
+  color:Color = Blue;
+  weapons:[Weapon];
+  equipped:Equipment;
+  path:[Vec3];
+}
+
+table Weapon {
+  name:string;
+  damage:short;
+}
+
+root_type Monster;