Update flatbuffers to v2.0.5 (#72132)
Summary:
This updates flatbuffer submodule from v1.12.1 to v2.0.5, but according to relnotes on [v2.0.0](https://github.com/google/flatbuffers/releases/tag/v2.0.0):
> Note, "2.0" doesn't signify any kind of major overhaul of FlatBuffers, it is merely trying to be more semver compatible, and this release does have breaking changes for some languages much like all releases before it.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72132
Reviewed By: seemethere
Differential Revision: D33923945
Pulled By: malfet
fbshipit-source-id: 9398d35f6bbc4ec05562a25f6ee444b66df94086
(cherry picked from commit 2335d5f69b0b0ee36ead7f5d66cfc47a1954f834)
