RFR: 8279640: ListView with null SelectionModel/FocusModel throws NPE [v3]

[Marius Hanl]

> This PR fixes a bunch of NPEs when a null `SelectionModel` or `FocusModel` is set on a `ListView`.
> 
> The following NPEs are fixed (all are also covered by exactly one test case):
> NPEs with null selection model:
> - Mouse click on a `ListCell`
> - SPACE key press
> - KP_UP (arrow up) key press
> - HOME key press
> - END key press
> - BACK_SLASH + CTRL key press
> 
> NPEs with null focus model:
> - SPACE key press
> - Select an items: getSelectionModel().select(1)
> - Clear-Select an item and add one after: listView.getSelectionModel().clearAndSelect(1); listView.getItems().add("3");

Marius Hanl has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jfx into 8279640-list-view-null-selection-focus-model
 - Fix NPE for null selection/focus -model in queryAccessibleAttribute(..)
 - Still set anchor when the selection model is null
 - Using global StageLoader
 - 8279640: ListView with null SelectionModel/FocusModel throws NPE

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/711/files
  - new: https://git.openjdk.org/jfx/pull/711/files/ffe781dd..9146e080

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=711&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=711&range=01-02

  Stats: 982567 lines in 11349 files changed: 579480 ins; 264970 del; 138117 mod
  Patch: https://git.openjdk.org/jfx/pull/711.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/711/head:pull/711

PR: https://git.openjdk.org/jfx/pull/711