Handle root offset and root table vtable invalidation (#7177)

* Handle invalid root offset

* Handle vtable offset invalidation

* Added script generator. Add more cases through vtable ref table size

* review responses

* vtable offset validation

* Moved padding insertion to the end. Tests invalid field lenghts

* table offsets validated. Added type after field

* validate string length

* add todo

* invalid vector length

* invalid structs

* general cleanup

* reworded invalid offsets

* example for vector of structs

* invalid vector of tables

* invalid vector of strings

* invalid vector of scalars

* vector of unions

* validate union type value

* invalid vector union type values

reflection/reflection.fbs

@@ -37,6 +37,7 @@ table Type {
     index:int = -1;  // If base_type == Object, index into "objects" below.
                      // If base_type == Union, UnionType, or integral derived
                      // from an enum, index into "enums" below.
+                     // If base_type == Vector && element == Union or UnionType.
     fixed_length:uint16 = 0;  // Only if base_type == Array.
     /// The size (octets) of the `base_type` field.
     base_size:uint = 4; // 4 Is a common size due to offsets being that size.