RFR: Merge jfx20 [v2]

[Kevin Rushforth]

> Merge `jfx20` 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 10 additional commits since the last revision:

 - Merge jfx20
 - 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
 - Merge
 - 8275033: Drag and drop a file produces NullPointerException Cannot read field "dragboard"
   
   Reviewed-by: kcr, angorya
 - 8137244: Empty Tree/TableView with CONSTRAINED_RESIZE_POLICY is not properly resized
   
   Reviewed-by: aghaisas
 - Merge
 - 8299681: Change JavaFX release version to 21
   
   Reviewed-by: arapte, angorya

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1020/files
  - new: https://git.openjdk.org/jfx/pull/1020/files/01fcdfe6..01fcdfe6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1020&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1020&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1020.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1020/head:pull/1020

PR: https://git.openjdk.org/jfx/pull/1020