RFR: 8254040: [testbug] Need additional regressions tests for ObservableList removeAll / retainAll

[Jeanette Winzenburg]

issue is about missing regressions tests for [JDK-8093144](https://bugs.openjdk.java.net/browse/JDK-8093144)

added tests for implementations of ObservableList that might be effected (FilteredList, selectedItems in ListView and
friends) - see bug report for details. Happily, the tests are passing with the current code base :) To see them failing
requires to replace the methods with invalid implementations (the bug report has a snippet that can be c&p'ed to
replace the correct version)

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Commit messages:
 - 8254040: [testbug] Need additional regressions tests for ObservableList

Changes: https://git.openjdk.java.net/jfx/pull/319/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=319&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254040
  Stats: 253 lines in 6 files changed: 253 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/319.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/319/head:pull/319

PR: https://git.openjdk.java.net/jfx/pull/319