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GH-33209: [C++] Support for reading JSON Datasets (#33732)

This adds initial support the JSON file format to the Dataset library. Since there's currently no public API for writing JSON files, this only deals with the reader-side facilities.
* Closes: #33209

Lead-authored-by: benibus <bpharks@gmx.com>
Co-authored-by: Ben Harkins <60872452+benibus@users.noreply.github.com>
Co-authored-by: Weston Pace <weston.pace@gmail.com>
Signed-off-by: Weston Pace <weston.pace@gmail.com>