RFR: 8296413: Tree/TableView with null focus model throws NPE in queryAccessibleAttribute()

[Andy Goryachev]

- added test to ensure no exception is thrown from Control.queryAccessibleAttribute() for all accessible attributes values
- fixed null focus model case in Tree/TableView

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Commit messages:
 - Merge remote-tracking branch 'origin/master' into
 - Merge branch '8187145.null.selection.model' into 8296413.query.accessible
 - Merge remote-tracking branch 'origin/master' into 8187145.null.selection.model
 - Merge branch '8187145.null.selection.model' into 8296413.query.accessible
 - Merge remote-tracking branch 'origin/master' into 8187145.null.selection.model
 - 8296413: cleanup
 - Merge branch '8187145.null.selection.model' into 8296413.query.accessible
 - Merge remote-tracking branch 'origin/master' into 8187145.null.selection.model
 - 8296413: query accessible
 - 8187145: cleanup
 - ... and 17 more: https://git.openjdk.org/jfx/compare/30147d2f...b88d3267

Changes: https://git.openjdk.org/jfx/pull/938/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=938&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296413
  Stats: 228 lines in 8 files changed: 181 ins; 26 del; 21 mod
  Patch: https://git.openjdk.org/jfx/pull/938.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/938/head:pull/938

PR: https://git.openjdk.org/jfx/pull/938