Make MonsterExtra table a root table (#5315)

- MonsterExtra table a root table
- add mosterdata_extra.json

tests/monster_extra.fbs

@@ -1,6 +1,6 @@
 namespace MyGame;
 
-// Not all programmining languages support this extra table.
+// Not all programming languages support this extra table.
 table MonsterExtra {
   // Float-point values with NaN and Inf defaults.
   testf_nan:float = nan;
@@ -9,4 +9,11 @@ table MonsterExtra {
   testd_nan:double = nan;
   testd_pinf:double = +inf;
   testd_ninf:double = -inf;
+  testf_vec : [float];
+  testd_vec : [double];
 }
+
+root_type MonsterExtra;
+
+file_identifier "MONE";
+file_extension "mon";