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GH-40824: [Java] Adding Spotless to Dataset module (#42062)

### Rationale for this change

Adding code style and formatting options for Dataset module. 

### What changes are included in this PR?

Code formatting spotless plugin has been added. 

### Are these changes tested?

Yes, but doesn't involve test cases, the plugin itself corrects. 
* GitHub Issue: #40824

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