GH-45694: [C++] Bump vendored flatbuffers to 24.3.6 (#45687)

### Rationale for this change

This bumps the vendored copy of flatbuffers to a version that also exists in the Meson wrapdb, which will subsequently make using the Meson build system easier

### What changes are included in this PR?

I have re-vendored flatbuffers keeping the namespacing modifications for arrow inplace. I have also regenerated the appropriate header files using flatc version 24.3.6

### Are these changes tested?

In CI

### Are there any user-facing changes?

I do not believe so

* GitHub Issue: #45694

Authored-by: Will Ayd <william.ayd@icloud.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>