RFR: Merge jfx20 [v2]

[Kevin Rushforth]

> Merge `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 five additional commits since the last revision:

 - Merge jfx20
 - 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/1010/files
  - new: https://git.openjdk.org/jfx/pull/1010/files/077c1e53..077c1e53

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1010&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1010&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1010.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1010/head:pull/1010

PR: https://git.openjdk.org/jfx/pull/1010