RFR: 8306121: Scene not rendered initially when changing scenes after fix for JDK-8296621 [v12]

[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 incrementally with one additional commit since the last revision:

  Antecipate request focus

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1110/files
  - new: https://git.openjdk.org/jfx/pull/1110/files/7828c2a9..c339b26c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=11
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1110&range=10-11

  Stats: 8 lines in 1 file changed: 4 ins; 4 del; 0 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