RFR: 8342098: Write a test to compare the images

[Naveen Narayanan]

This testcase checks for the following:

1. An image is drawn on the screen and a portion of it is captured using a Robot. It is tested by comparing whether the captured image is same as the source image. 

Testing:
Tested using Mach5(20 times per platform) in MacOS, Linux and Windows. Seen all tests passing.

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Commit messages:
 - 8342098: Write a test to compare the images

Changes: https://git.openjdk.org/jdk/pull/21524/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21524&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342098
  Stats: 162 lines in 1 file changed: 162 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21524.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21524/head:pull/21524

PR: https://git.openjdk.org/jdk/pull/21524