RFR: 8342098: Write a test to compare the images [v3]

[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.

Naveen Narayanan has updated the pull request incrementally with one additional commit since the last revision:

  8342098: Updated review comments

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21524/files
  - new: https://git.openjdk.org/jdk/pull/21524/files/215d1d03..98e2a732

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21524&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21524&range=01-02

  Stats: 21 lines in 1 file changed: 4 ins; 13 del; 4 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