RFR: 8274932: Render scales in EmbeddedWindow are not properly updated [v5]

[Prasanta Sadhukhan]

> When the JavaFX scene is set before it is really shown, then the scale factors are not properly propagated to the EmbeddedWindow, resulting in showing wrong scales.
> Fix is made to update scales to EmbeddedWindow

Prasanta Sadhukhan 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 six additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jfx into JDK-8274932
 - Fix to get correct scale in secondary monitor
 - Set stage scale in FX thread
 - Set stage scale in FX thread
 - Set stage scale in FX thread
 - 8274932: Render scales in EmbeddedWindow are not properly updated

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1171/files
  - new: https://git.openjdk.org/jfx/pull/1171/files/6bfb624c..c2c23fc5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1171&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1171&range=03-04

  Stats: 70526 lines in 1267 files changed: 30933 ins; 13657 del; 25936 mod
  Patch: https://git.openjdk.org/jfx/pull/1171.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1171/head:pull/1171

PR: https://git.openjdk.org/jfx/pull/1171