RFR: 8306121: Scene not rendered initially when changing scenes after fix for JDK-8296621 [v13]

[Thiago Milczarek Sayao]

> I replicated the fix on #1054 on Linux.
> 
> Also fixes [Monocle: Stage no longer gets focus after fix for JDK-8296621](https://bugs.openjdk.org/browse/JDK-8304734)

Thiago Milczarek Sayao 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 55 additional commits since the last revision:

 - Merge branch 'master' into change_scene_fix
 - Antecipate request focus
 - Merge branch 'master' into change_scene_fix
 - Fix ComboBoxTest
 - Add manual test
 - Merge branch 'master' into change_scene_fix
 - Merge branch 'openjdk:master' into master
 - Merge branch 'master' into change_scene_fix
 - Merge remote-tracking branch 'origin/master'
 - Review changes
 - ... and 45 more: https://git.openjdk.org/jfx/compare/b63e2fd8...15a08963

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1110/files
  - new: https://git.openjdk.org/jfx/pull/1110/files/c339b26c..15a08963

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=12
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=11-12

  Stats: 1051 lines in 40 files changed: 628 ins; 158 del; 265 mod
  Patch: https://git.openjdk.org/jfx/pull/1110.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1110/head:pull/1110

PR: https://git.openjdk.org/jfx/pull/1110