RFR: 8280951: Testbug: fix commented asserts in XXViewTest.test_rt_29650

[Jeanette Winzenburg]

the issue was commented asserts in a test methods - they had been failing due to incorrect usage of registering an edit commit handler

fix was to correct the registration and uncomment the assert (ListViewTest). For Tree/TableViewTest, had to adjust value access also (was: c&p from ListViewTest). Verified that the uncommented (corrected) asserts are failing/passing before/after fix of test bug

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Commit messages:
 - 8280951: Testbug: fix commented asserts in XXViewTest.test_rt_29650

Changes: https://git.openjdk.java.net/jfx/pull/725/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=725&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280951
  Stats: 10 lines in 3 files changed: 0 ins; 3 del; 7 mod
  Patch: https://git.openjdk.java.net/jfx/pull/725.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/725/head:pull/725

PR: https://git.openjdk.java.net/jfx/pull/725