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ARROW-17480: [Java] add setNull() to FieldVector interface (#14244)

Implemented setNull for vector types where it was not supported (including the abstract ExtensionTypeVector class), and added it to the FieldVector interface.

The change makes it possible to call setNull() on arbitrary field vectors without casting. 

Lead-authored-by: Larry White <ljw1001@gmail.com>
Co-authored-by: Larry White <lwhite1@users.noreply.github.com>
Signed-off-by: David Li <li.davidm96@gmail.com>