[jdk21u-dev] RFR: 8313697: [XWayland][Screencast] consequent getPixelColor calls are slow

[Martin Doerr]

Clean backport of [JDK-8313697](https://bugs.openjdk.org/browse/JDK-8313697) and [JDK-8310334](https://bugs.openjdk.org/browse/JDK-8310334) which belong together.

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Commit messages:
 - Backport 2f04bc5f934887029d8bcc13cf722d8498a35120

Changes: https://git.openjdk.org/jdk21u-dev/pull/743/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=743&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313697
  Stats: 171 lines in 7 files changed: 121 ins; 23 del; 27 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/743.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/743/head:pull/743

PR: https://git.openjdk.org/jdk21u-dev/pull/743