Manually cherry-pick fix for creating vectors of structs

This pulls in the functional fix in google/flatbuffers#7883

This fixes creation of vectors of structs with the "raw" flatbuffer API.
I observed this when writing tests for the static flatbuffer API and
discovering a discrepancy where the static flatbuffer API behaved
correctly and the existing API did not.

Change-Id: I124192b7f23cad4ae9b50366921ddb4e6a2590cd
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>

third_party/flatbuffers/include/flatbuffers/flatbuffer_builder.h

@@ -787,7 +787,7 @@ class FlatBufferBuilder {
   /// where the vector is stored.
   template<typename T>
   Offset<Vector<const T *>> CreateVectorOfStructs(const T *v, size_t len) {
-    StartVector(len * sizeof(T) / AlignOf<T>(), sizeof(T), AlignOf<T>());
+    StartVector(len, sizeof(T), AlignOf<T>());
     if (len > 0) {
       PushBytes(reinterpret_cast<const uint8_t *>(v), sizeof(T) * len);
     }
@@ -1211,7 +1211,7 @@ class FlatBufferBuilder {
   // Allocates space for a vector of structures.
   // Must be completed with EndVectorOfStructs().
   template<typename T> T *StartVectorOfStructs(size_t vector_size) {
-    StartVector(vector_size * sizeof(T) / AlignOf<T>(), sizeof(T), AlignOf<T>());
+    StartVector(vector_size, sizeof(T), AlignOf<T>());
     return reinterpret_cast<T *>(buf_.make_space(vector_size * sizeof(T)));
   }