RFR: 8307779: Relax the java.awt.Robot specification

[Alexander Zvegintsev]

We need to relax the java.awt.Robot specification according to the latest operating system trends. 
This should at least cover the case of Wayland, which has changed many familiar concepts in Linux.

https://bugs.openjdk.org/browse/JDK-8280982 [Wayland] [XWayland] java.awt.Robot taking screenshots
https://bugs.openjdk.org/browse/JDK-8280995 [XWayland] Robot.mouseMove does not visually move mouse cursor
https://bugs.openjdk.org/browse/JDK-8280990 [XWayland] XTest emulated mouse click does not bring window to front.
https://bugs.openjdk.org/browse/JDK-8280988 [XWayland] Click on title to request focus test failures

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Commit messages:
 - update documentation
 - upd
 - update also for createScreenCapture
 - update based on a review comments
 - doc changes

Changes: https://git.openjdk.org/jdk/pull/13809/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13809&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307779
  Stats: 103 lines in 2 files changed: 99 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/13809.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13809/head:pull/13809

PR: https://git.openjdk.org/jdk/pull/13809