RFR: 8090123: Items are no longer visible when collection is changed

Fri Feb 17 12:53:05 UTC 2023

When a large number of items were scrolled in the `ChoiceBox`, the scrolled offset was carried forward when the list is replaced with small number of items. Hence the scroll up arrow was displayed with empty popup.

Changed code to scroll to top before popup display when content height of `ChoiceBox` is smaller than the scrolled offset.

Added system test to validate the fix.

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Commit messages:
 - Adding blank line after comment
 - ChoiceBox items display issue fix

Changes: https://git.openjdk.org/jfx/pull/1039/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1039&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8090123
  Stats: 199 lines in 3 files changed: 199 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1039.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1039/head:pull/1039

PR: https://git.openjdk.org/jfx/pull/1039