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GH-40405: [C++] Produce better error message when Move is attempted on flat-namespace accounts (#40406)

### Rationale for this change

To guide users that might try to `Move` on accounts without HNS.

### What changes are included in this PR?

The rewrite of the error message.

### Are these changes tested?

Covered by existing tests.
* GitHub Issue: #40405

Authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>