RFR: 7148092: [macosx] When Alt+down arrow key is pressed, the combobox popup does not appear.

[Prasanta Sadhukhan]

On Thu, 25 Aug 2022 07:24:17 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

> When comboBox have focus, pressing Alt+Down (or Up) should render the popup which is not happening for Aqua L&F.
> 
> Fix is to add toggleAction for Alt+Down/Up keys as has been done for [MetalLookAndFeel](https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/metal/MetalLookAndFeel.java#L912)
> 
> closed problemlisted test is used to check the fix.

It seems macos native combox does something extra. 
When Alt+Down is pressed on combobox, it opens up the popup but if the popup is already opened, it selects the last entry.
When Alt+Up is pressed on combobox, it opens up the popup but if the popup is already opened, it selects the first entry.

Modified the fix to behave same as native combobox.

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PR: https://git.openjdk.org/jdk/pull/10014