RFR: 8155030: The Menu Mnemonics are always displayed for GTK LAF [v2]

[Tejesh R]

On Wed, 8 May 2024 05:53:38 GMT, Abhishek Kumar <abhiscxk at openjdk.org> wrote:

>> In GTK LAF, the menu mnemonics are always displayed which is different from the native behavior. In native application **(tested with gedit**), the menu mnemonics toggle on press of `ALT` key. Menu mnemonics are hidden initially and then toggles between show/hide on `ALT` press. 
>> Proposed fix is to handle the `ALT` key press for GTK LAF and mimic the native behavior. Fix is similar to the `ALT` key processing in  Windows LAF. Automated test case is added to verify the fix and tested in Ubuntu and Oracle linux.
>> 
>> CI testing is green and link attached in JBS.
>
> Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Var moved to local scope

`postProcessKeyEvent(KeyEvent ev)` method from `AquaMnemonicHandler` class is reused instead of `WindowsRootPaneUI` class, any reason for that? (Since I see some differences in the way they are processing the event).

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PR Review: https://git.openjdk.org/jdk/pull/18992#pullrequestreview-2044789195