[C++] Use System Provided Flatbuffers

[WillAyd]

Describe the enhancement requested

Right now the project strictly requires the vendored version of flatbuffers, and places static assertions on main that the version of flatbuffers being used is 23.5.26

Instead of forcing the use of the vendored copy, we could open the project up to detecting a system dependency first, only falling back to the vendored copy when none is detected.

The origin of this conversation stems from the setup of the Meson build system in #45596 (comment)

@kou

Component(s)

C++

[WillAyd]

So the more I've looked at this I've started to question if its worth the effort. From what I can read, it is a hard requirement for flatbuffers that the compiler and runtime versions match exactly. The odds of that are pretty low, so maybe not worth all of the extra CMake work here?

@kou

[kou]

I thought this is one of blockers of Meson support. If so, I'll take a look at this.

[WillAyd]

I think the easiest path to Meson support would be to upgrade the vendored flatbuffers that CMake uses to a version that also exists in Meson's WrapDB. I'll investigate that further

[kou]

OK. Could you open a separated issue for upgrading the vendored Flatbuffers?
We may work on using system provided Flatbuffers later.

[WillAyd]

Makes sense - see #45694