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

[Ajit Ghaisas]

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

-------------

Commit messages:
 - add missed @Test tag
 - fix ignored unit tests

Changes: https://git.openjdk.java.net/jfx/pull/466/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=466&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265439
  Stats: 41 lines in 1 file changed: 16 ins; 18 del; 7 mod
  Patch: https://git.openjdk.java.net/jfx/pull/466.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/466/head:pull/466

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