RFR: 8265439: [TestBug] Enable and fix ignored unit tests in MenuItemTest

[Kevin Rushforth]

On Mon, 19 Apr 2021 12:51:06 GMT, Ajit Ghaisas <aghaisas at openjdk.org> wrote:

> This PR enables ignored unit tests from MenuItemTest and fixes them.
> 4 ignored tests are fixed. 
> 2 ignored tests are removed.
> 2 new tests are added.
> 
> **Before fix :**
> total tests = 89
> failures = 0
> ignored tests =  6
> 
> **After fix :**
> total tests = 89
> failures = 0
> ignored tests =  0

Thanks for the evaluation. I only have one remaining question on the tests that now expect NPE.

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PR: https://git.openjdk.java.net/jfx/pull/466