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ARROW-15300: [C++] Update Skyhook for async dataset interfaces

After the synchronous dataset interfaces were removed in ARROW-13554, we need to update Skyhook to use the async interfaces. For now, we just use the same synchronous path as before, but on an I/O thread.

Closes #12123 from lidavidm/arrow-15300

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>