Fix model generation of array with items unique = true

[MelleD]

Fix model generation of array with items unique = true as Java Set. Also fix the default values handling for Sets.

Fix #18102

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  @cachescrubber (2022/02) @welshm (2022/02) @MelleD (2022/02) @atextor (2022/02) @manedev79 (2022/02) @javisst (2022/02) @borsch (2022/02) @banlevente (2022/02) @Zomzog (2022/09) @martin-mfg (2023/08)

[wing328]

thanks for the fix

fyi @OpenAPITools/generator-core-team