RFR: 8327478: Add System test to verify TextSelection issue for webkit-617.1 [v4]

[Gopal Pattnaik]

> There was no test included with the fix for [JDK-8326989](https://bugs.openjdk.org/browse/JDK-8326989),
> 
> Hence we are adding a system test now.
> 
> Test is written as 
> 1. Load html content in web view.
> 2. pick the color of mouse pointer.
> 3. Perform double click.
> 4. pick the color again.
>> expected bahaviour: colour picked in step 2 and 4 should not match.
> 
> Verification:
> The test passes with latest webkit source
> Also verified that test fails when the fix for [JDK-8326989](https://bugs.openjdk.org/browse/JDK-8326989) is reverted.

Gopal Pattnaik has updated the pull request incrementally with one additional commit since the last revision:

  Addressed Review comments

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1719/files
  - new: https://git.openjdk.org/jfx/pull/1719/files/b4836243..d05cbf08

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1719&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1719&range=02-03

  Stats: 10 lines in 1 file changed: 0 ins; 2 del; 8 mod
  Patch: https://git.openjdk.org/jfx/pull/1719.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1719/head:pull/1719

PR: https://git.openjdk.org/jfx/pull/1719