RFR: 4795384: GTK+ JFileChooser buttons should have mnemonics

[Tejesh R]

On Fri, 16 Aug 2024 09:59:26 GMT, Abhishek Kumar <abhiscxk at openjdk.org> wrote:

> JFileChooser don't have the mnemonics for open and save button in GTK L&F. Fix is to add mnemonics for open and save button.
> Fix can be verified by Swingset2 demo application. Mnemonics in GTK L&F are visible once alt key is pressed.
> After running the SwingSet2 application, change the `L&F to GTK` and select` JFileChooser demo` from toolbar. Click on `Select Plain JFileChooser` button and then press alt key to verify the mnemonics.

Adding a test for this fix would be better, I guess.......

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PR Review: https://git.openjdk.org/jdk/pull/20612#pullrequestreview-2242565978