RFR: 8292353: TableRow vs. TreeTableRow: inconsistent visuals in cell selection mode

[Andy Goryachev]

The issue is caused by TreeTableRow incorrectly selected when cell selection mode is enabled.

Changes:
- modified TreeTableRow.updateSelection()

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Commit messages:
 - 8292353: update selection

Changes: https://git.openjdk.org/jfx/pull/875/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=875&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292353
  Stats: 10 lines in 1 file changed: 5 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jfx/pull/875.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/875/head:pull/875

PR: https://git.openjdk.org/jfx/pull/875