RFR: 8367991: Update RegionBackground tests to use ScreenCaptureTestWatcher utility [v2]

[Jayathirth D V]

> We are seeing very rare intermittent failures in RegionBackgroundFillUITest & RegionBackgroundImageUITest tests in linux. We already have [JDK-8328217](https://bugs.openjdk.org/browse/JDK-8328217) to fix this issue.
> 
> To identify the root cause better, we want to capture the test content when it is failing using ScreenCaptureTestWatcher utility.
> 
> Since we wan to capture the test window before test stage is cleared. We are now clearing the test stage and next test setup. Initially tried updating this behaviour in `VisualTestBase` itself, but that causes tests like `test.robot.test3d.PointLightIlluminationTest` as it overrides the test setup functions.
> 
> This change is tested to make sure ScreenCaptureTestWatcher takes appropriate screen capture on failure and CI full headful test run is green.

Jayathirth D V has updated the pull request incrementally with one additional commit since the last revision:

  Add missing initialization logic

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1913/files
  - new: https://git.openjdk.org/jfx/pull/1913/files/00661199..675e3e04

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1913&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1913&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1913.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1913/head:pull/1913

PR: https://git.openjdk.org/jfx/pull/1913