RFR: 8378153: Robot.getPixelColor() may return stale pixels due to missing Toolkit.sync()

[Sergey Bylokhov]

Robot.getPixelColor() does not call Toolkit.getDefaultToolkit().sync() before reading the pixel, unlike Robot.createScreenCapture() which has had this call since [JDK-6725214](https://bugs.openjdk.org/browse/JDK-6725214).

When a hardware-accelerated pipeline (OGL, D3D, Metal) is active, rendering may be buffered and not yet flushed to the screen when getPixelColor() reads the pixel. This causes it to return stale values typically the window background color instead of the rendered content.

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Commit messages:
 - 8378153: Robot.getPixelColor() may return stale pixels due to missing Toolkit.sync()

Changes: https://git.openjdk.org/jdk/pull/29780/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29780&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378153
  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29780.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29780/head:pull/29780

PR: https://git.openjdk.org/jdk/pull/29780