RFR: 8292062: misc javax/swing tests failing

[Prasanta Sadhukhan]

In [PR#9488](https://github.com/openjdk/jdk/pull/9488) https://git.openjdk.org/jdk/commit/b2f0cbdca109507e5f8e0c185f601c0c1e31f4fb
`CTRL+ALT` mnemonic support was added for Nimbus in macOS instead of `Alt`

so 2 of the 3 tests were failing after that, as it has workaround for non-support of CTRL+ALT mnemonic in macos for Nimbus L&F.
That workaround is now removed for the tests to now pass.

For RightAltKey test failure, we should have ALT_GRAPH mask for Menu.shortcutKeys also,
 as it is done for
https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicLookAndFeel.java#L1101

so ALT_GRAPH support was added for Nimbus Menu.shortcutKeys

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

Commit messages:
 - 8292062: misc javax/swing tests failing

Changes: https://git.openjdk.org/jdk/pull/9808/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9808&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292062
  Stats: 9 lines in 4 files changed: 2 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/9808.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9808/head:pull/9808

PR: https://git.openjdk.org/jdk/pull/9808