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GH-44506: [Docs][C++] Fix documentation directive for ChunkLocation (#44505)

### Rationale for this change

Since ChunkLocation is a typedef/alias, it needs to use the `doxygentypedef` Sphinx directive rather than `doxygenstruct` in order for it to show up in the generated HTML. Otherwise we get an error.

### What changes are included in this PR?

Just docs:

- Replace `doxygenstruct` directive with `doxygentypedef`
- Remove `:members:` directive as it's not needed

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes, though just docs.
* GitHub Issue: #44506

Authored-by: Bryce Mecum <petridish@gmail.com>
Signed-off-by: Bryce Mecum <petridish@gmail.com>