RFR: JDK-8210547 synchronise with OpenGL after the last window is presented [v2]

[notzed]

> As discussed on the mailing list.
> 
> OpenGL requires an explicit glFinish() to synchronise with the video refresh.  The current usage is incorrect and against the specification.  This patch calls glFinish() after all windows have been drawn following a pulse.

notzed has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  JDK-8210547 synchronise with OpenGL after the last window is presented

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1981/files
  - new: https://git.openjdk.org/jfx/pull/1981/files/34a06fdc..293c5712

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1981&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1981&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1981.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1981/head:pull/1981

PR: https://git.openjdk.org/jfx/pull/1981