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GH-40832: [Java] Adding Spotless to Vector module (#42061)

### Rationale for this change

Applying Java code style and formatting options to Vector module.

### What changes are included in this PR?

Java code formatting via spotless plugin has been enabled.

Address some missing javadoc comments violations in *StructVector classes caused by a change in the number of lines for the impacted methods.

### Are these changes tested?

Yes, but doesn't involve test cases, the plugin itself corrects.

### Are there any user-facing changes?

No

* GitHub Issue: #40832

Authored-by: Laurent Goujon <laurent@apache.org>
Signed-off-by: David Li <li.davidm96@gmail.com>