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GH-38701: [C++][FS][Azure] Implement `DeleteDirContents()` (#38888)

### Rationale for this change

`DeleteDirContents()` deletes the given directory contents recursively like other filesystem implementations.

Azure file system treats the following cases as root directory:
* Empty container
* Empty path

### What changes are included in this PR?

List and delete approach is used with/without hierarchical namespace support. Because Azure doesn't provide "DeleteDirContents" API with hierarchical namespace support. We may want to use delete the given directory and create an empty approach instead of list and delete approach for performance but it may not be acceptable with some use cases. 

### Are these changes tested?

Yes.

### Are there any user-facing changes?

Yes.
* Closes: #38701

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>