Add static asserts to ensure that reflection API arrays are kept in sync (#5934)

* Add static asserts to ensure that reflection API arrays are kept in sync

* Move changes from generated file into source fbs file

* Rename enum value and regenerate reflection_generated.h

* Add comments to each entries of type sizes array

include/flatbuffers/reflection.h

@@ -46,7 +46,30 @@ inline bool IsLong(reflection::BaseType t) {
 // Size of a basic type, don't use with structs.
 inline size_t GetTypeSize(reflection::BaseType base_type) {
   // This needs to correspond to the BaseType enum.
-  static size_t sizes[] = { 0, 1, 1, 1, 1, 2, 2, 4, 4, 8, 8, 4, 8, 4, 4, 4, 4 };
+  static size_t sizes[] = {
+    0, // None
+    1, // UType
+    1, // Bool
+    1, // Byte
+    1, // UByte
+    2, // Short
+    2, // UShort
+    4, // Int
+    4, // UInt
+    8, // Long
+    8, // ULong
+    4, // Float
+    8, // Double
+    4, // String
+    4, // Vector
+    4, // Obj
+    4, // Union
+    0, // Array. Only used in structs. 0 was chosen to prevent out-of-bounds errors.
+
+    0  // MaxBaseType. This must be kept the last entry in this array.
+    };
+  static_assert(sizeof(sizes) / sizeof(size_t) == reflection::MaxBaseType + 1,
+                "Size of sizes[] array does not match the count of BaseType enum values.");
   return sizes[base_type];
 }