RFR: 8232524: SynchronizedObservableMap cannot be be protected for copying/iterating

[Robert Lichtenberger]

By using the collection itself as synchronization lock we achieve behaviour that matches java.util.Collections classes.

I've create test cases that fail with the current way of synchronizing on a separate object.

I've removed unused constructors.

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

Commits:
 - 7e80839f: 8232524: SynchronizedObservableMap cannot be be protected for copying/iterating
 - 8ecf3545: JDK-8232524 fixed.

Changes: https://git.openjdk.java.net/jfx/pull/17/files
 Webrev: https://webrevs.openjdk.java.net/jfx/17/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8232524
  Stats: 120 lines in 2 files changed: 95 ins; 17 del; 8 mod
  Patch: https://git.openjdk.java.net/jfx/pull/17.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/17/head:pull/17

PR: https://git.openjdk.java.net/jfx/pull/17