RFR: 7148092: [macosx] When Alt+down arrow key is pressed, the combobox popup does not appear. [v4]

[Prasanta Sadhukhan]

> When comboBox have focus, pressing Alt+Down (or Up) should render the popup which is not happening for Aqua L&F.
> 
> Fix is to add toggleAction for Alt+Down/Up keys as has been done for [MetalLookAndFeel](https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/javax/swing/plaf/metal/MetalLookAndFeel.java#L912)
> 
> closed problemlisted test is used to check the fix.

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  Add test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10014/files
  - new: https://git.openjdk.org/jdk/pull/10014/files/531dec1f..180f73d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10014&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10014&range=02-03

  Stats: 121 lines in 2 files changed: 102 ins; 8 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/10014.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10014/head:pull/10014

PR: https://git.openjdk.org/jdk/pull/10014