RFR: 8299522: Incorrect size of Approve button in custom JFileChooser [v12]

[Tejesh R]

On Tue, 17 Jan 2023 05:37:38 GMT, Tejesh R <tr at openjdk.org> wrote:

>> FileChooser Open/Approve button size is shown incorrectly when no Approve button text is set in `CUSTOM_DIALOG` type. Reason being that no default Approve Button text is returned during Dialog Type Property change. Since `null` is returned as Button string the Button size is incorrectly shown. The fix here addresses the issue by adding a default Approve Button Text when no text is set explicitly in case of `CUSTOM_DIALOG` type.
>> Automated test is attached which has been tested with multiple test runs.
>
> Tejesh R has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused imports

I will check both tooltip and mnemonic validation and update the PR.

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PR: https://git.openjdk.org/jdk/pull/11901