RFR: 8306121: Scene not rendered initially when changing scenes after fix for JDK-8296621 [v6]

[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 46 additional commits since the last revision:

 - Review changes
 - Merge branch 'master' into change_scene_fix
 - Change call to requestFocus
 - Revert "The window could start iconified."
   
   This reverts commit f92e25cbcc24fd772b9d6bb25a92386ec0561313.
 - The window could start iconified.
 - Request Focus on setVisible
 - fix mistake
 - Scene not rendered initially when changing scenes after fix for JDK-8296621
 - Merge branch 'openjdk:master' into master
 - Merge branch 'openjdk:master' into master
 - ... and 36 more: https://git.openjdk.org/jfx/compare/750bc278...2649d15c

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1110/files
  - new: https://git.openjdk.org/jfx/pull/1110/files/f4a24eff..2649d15c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=05
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=04-05

  Stats: 28 lines in 7 files changed: 4 ins; 12 del; 12 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