RFR: Merge jfx20 [v2]

[Kevin Rushforth]

> Merfe `jfx20` branch into `master`.

Kevin Rushforth 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 15 additional commits since the last revision:

 - Merge jfx20
 - 8290092: Temporary files are kept when call Clipboard.getSystemClipboard().getImage()
   
   Reviewed-by: aghaisas
 - 8290765: Remove parent disabled/treeVisible listeners
   
   Reviewed-by: arapte, jhendrikx, nlisker
 - 8138842: TableViewSelectionModel.selectIndices does not select index 0
   
   Reviewed-by: angorya, aghaisas
 - 8298382: JavaFX ChartArea Accessibility Reader
   
   Reviewed-by: kcr, angorya
 - Merge
 - 8251862: Wrong position of Popup windows at the intersection of 2 screens
   
   Reviewed-by: aghaisas, arapte
 - 8301604: Replace Collections.unmodifiableList with List.of
   
   Reviewed-by: nlisker
 - 8299977: Update WebKit to 615.1
   
   Co-authored-by: Jay Bhaskar <jbhaskar at openjdk.org>
   Reviewed-by: kcr, sykora
 - 8237505: RadioMenuItem in ToggleGroup: deselected on accelerator
   
   Reviewed-by: angorya, aghaisas
 - ... and 5 more: https://git.openjdk.org/jfx/compare/a1d82e11...b9b2ba04

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1028/files
  - new: https://git.openjdk.org/jfx/pull/1028/files/b9b2ba04..b9b2ba04

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1028&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1028&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1028.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1028/head:pull/1028

PR: https://git.openjdk.org/jfx/pull/1028