RFR: 8234315: GTK LAF does not gray out disabled JMenu

[Abhishek Kumar]

On Thu, 8 Sep 2022 03:42:49 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> Looks fine, please double how it will work if the dark theme is set.

In case of dark theme set, foreground color is grayed out. 
![Enabled_Menu_Dark_Theme](https://user-images.githubusercontent.com/107542245/189043107-3393c933-d868-4834-8f3b-e2254969cac7.png)

![Disabled_Menu_Dark_Theme](https://user-images.githubusercontent.com/107542245/189043132-45b75066-083e-4220-adbf-8947c7ee7e43.png)

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PR: https://git.openjdk.org/jdk/pull/10176