RFR: 8264157: Items of non-editable ComboBox cannot be selected using up/down keys

[Ambarish Rapte]

This issue [JDK-8264157](https://bugs.openjdk.java.net/browse/JDK-8264157) is a regression of [JDK-8209788](https://bugs.openjdk.java.net/browse/JDK-8209788), which removed two KeyMappings from `ComboBoxListViewBehavior`. That removal was not required to fix [JDK-8209788](https://bugs.openjdk.java.net/browse/JDK-8209788).
Reverting `ComboBoxListViewBehavior.java` fixes the regression.
Fix includes a new test which fails before and pass with the fix.

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Commit messages:
 - revert partial fix and add test

Changes: https://git.openjdk.java.net/jfx/pull/485/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=485&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264157
  Stats: 69 lines in 2 files changed: 67 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/485.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/485/head:pull/485

PR: https://git.openjdk.java.net/jfx/pull/485