RFR: 8218474: JComboBox display issue with GTKLookAndFeel

[Tejesh R]

On Wed, 7 Dec 2022 10:25:31 GMT, Abhishek Kumar <abhiscxk at openjdk.org> wrote:

> In case of GTK LAF, the current selected element was not visible due to arrowbutton is rendered in entire display area of Combobox.
> 
> The proposed fix is to set the `squareButton `property of combobox to `false `so that the arrowbutton didn't take entire combobox display area for rendering. The `getMinimumSize `method is overridden in `SynthComboBoxUI `to consider **arrowbutton insets** for combobox minimum size. 
> 
> The JCK tests mentioned in JBS seems fine with the fix. 
> An automated test case is implemented to test in Nimbus and GTK LAF. The text color check is to ensure the current selected item is visible.
> 
> When swing tests are run with LAF set to Nimbus and GTK LAF, few test failures observed. 
> 
> Although CI jobs looks ok with tests run in their default set LAFs.
> 
> `open/test/jdk/javax/swing/JComboBox/TestComboBoxHeight.java` test passes if run in GTK LAF with current fix.

Marked as reviewed by tr (Committer).

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PR: https://git.openjdk.org/jdk/pull/11555