FlatBuffers 64 for C++ (#7935)

* First working hack of adding 64-bit. Don't judge :)

* Made vector_downward work on 64 bit types

* vector_downward uses size_t, added offset64 to reflection

* cleaned up adding offset64 in parser

* Add C++ testing skeleton for 64-bit

* working test for CreateVector64

* working >2 GiB buffers

* support for large strings

* simplified CreateString<> to just provide the offset type

* generalize CreateVector template

* update test_64.afb due to upstream format change

* Added Vector64 type, which is just an alias for vector ATM

* Switch to Offset64 for Vector64

* Update for reflection bfbs output change

* Starting to add support for vector64 type in C++

* made a generic CreateVector that can handle different offsets and vector types

* Support for 32-vector with 64-addressing

* Vector64 basic builder + tests working

* basic support for json vector64 support

* renamed fields in test_64bit.fbs to better reflect their use

* working C++ vector64 builder

* Apply --annotate-sparse-vector to 64-bit tests

* Enable Vector64 for --annotate-sparse-vectors

* Merged from upstream

* Add `near_string` field for testing 32-bit offsets alongside

* keep track of where the 32-bit and 64-bit regions are for flatbufferbuilder

* move template<> outside class body for GCC

* update run.sh to build and run tests

* basic assertion for adding 64-bit offset at the wrong time

* started to separate `FlatBufferBuilder` into two classes, 1 64-bit aware, the other not

* add test for nested flatbuffer vector64, fix bug in alignment of big vectors

* fixed CreateDirect method by iterating by Offset64 first

* internal refactoring of flatbufferbuilder

* block not supported languages in the parser from using 64-bit

* evolution tests for adding a vector64 field

* conformity tests for adding/removing offset64 attributes

* ensure test is for a big buffer

* add parser error tests for `offset64` and `vector64` attributes

* add missing static that GCC only complains about

* remove stdint-uintn.h header that gets automatically added

* move 64-bit CalculateOffset internal

* fixed return size of EndVector

* various fixes on windows

* add SizeT to vector_downward

* minimze range of size changes in vector and builder

* reworked how tracking if 64-offsets are added

* Add ReturnT to EndVector

* small cleanups

* remove need for second Array definition

* combine IndirectHelpers into one definition

* started support for vector of struct

* Support for 32/64-vectors of structs + Offset64

* small cleanups

* add verification for vector64

* add sized prefix for 64-bit buffers

* add fuzzer for 64-bit

* add example of adding many vectors using a wrapper table

* run the new -bfbs-gen-embed logic on the 64-bit tests

* remove run.sh and fix cmakelist issue

* fixed bazel rules

* fixed some PR comments

* add 64-bit tests to cmakelist

include/flatbuffers/base.h

@@ -43,6 +43,7 @@
 #include <vector>
 #include <set>
 #include <algorithm>
+#include <limits>
 #include <iterator>
 #include <memory>
 
@@ -323,9 +324,11 @@ namespace flatbuffers {
 // Also, using a consistent offset type maintains compatibility of serialized
 // offset values between 32bit and 64bit systems.
 typedef uint32_t uoffset_t;
+typedef uint64_t uoffset64_t;
 
 // Signed offsets for references that can go in both directions.
 typedef int32_t soffset_t;
+typedef int64_t soffset64_t;
 
 // Offset/index used in v-tables, can be changed to uint8_t in
 // format forks to save a bit of space if desired.
@@ -334,7 +337,8 @@ typedef uint16_t voffset_t;
 typedef uintmax_t largest_scalar_t;
 
 // In 32bits, this evaluates to 2GB - 1
-#define FLATBUFFERS_MAX_BUFFER_SIZE ((1ULL << (sizeof(::flatbuffers::soffset_t) * 8 - 1)) - 1)
+#define FLATBUFFERS_MAX_BUFFER_SIZE std::numeric_limits<::flatbuffers::soffset_t>::max()
+#define FLATBUFFERS_MAX_64_BUFFER_SIZE std::numeric_limits<::flatbuffers::soffset64_t>::max()
 
 // The minimum size buffer that can be a valid flatbuffer.
 // Includes the offset to the root table (uoffset_t), the offset to the vtable