RFR: 8054572: [macosx] JComboBox paints the border incorrectly

[Damon Nguyen]

When a JComboBox is editable, the button segment of the combo box is misaligned vertically and has a different height. This change fixes these issues and adds a manual test that checks the appearance of an editable and non-editable JComboBox.

One of the discussions revolving this issue is the native macOS appearance of editable JComboBoxes. After looking through native macOS apps, the only one found is in System Preferences > Date & Time. The problem here is that the native equivalent found here uses a blue button with a single down arrow as the button's symbol. The current swing implementation uses a white button with an up & down arrow symbol for the button. A JRS widget button that has this blue button with a single downward arrow exists but does not support text fields.

As such, I believe the best fix for this issue is to mainly fix the alignment and sizing issue. I looked through Apple's documentation for these UI elements but editable JComboBoxes aren't specifically listed anywhere. Similarly, there's barely any editable JComboBoxes used in native mac apps (only the date & time). So, I don't think it's a major issue if JComboBox does not exactly match the example found in Date & Time.

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Commit messages:
 - Updated test with PassFailJFrame
 - Added test
 - Adjusted height and coordinate for editable JComboBox

Changes: https://git.openjdk.org/jdk/pull/9473/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9473&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8054572
  Stats: 100 lines in 2 files changed: 99 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9473.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9473/head:pull/9473

PR: https://git.openjdk.org/jdk/pull/9473