RFR: 7124287: [TEST_BUG] [macosx] JTableHeader doesn't get focus after pressing F8 key

[Prasanta Sadhukhan]

JTableHeader doesn't get focus after pressing F8 key in macos causing test to fail. Added F8 keybindings to macos similar to 
MetalLookAndFeel
https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/metal/MetalLookAndFeel.java#L1232
and BasicLookAndFeel
https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicLookAndFeel.java#L1497

Test is moved from closed to open and now passing in macos.

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Commit messages:
 - 7124287: [TEST_BUG] [macosx] JTableHeader doesn't get focus after pressing F8 key

Changes: https://git.openjdk.java.net/jdk/pull/6019/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6019&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-7124287
  Stats: 75 lines in 2 files changed: 74 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6019.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6019/head:pull/6019

PR: https://git.openjdk.java.net/jdk/pull/6019