RFR: 8187759: Background not refreshed when painting over a transparent JFrame [v3]

[Tejesh R]

> This is happening in linux where `BuffereStrategyPaintManager` is used to paint to offscreen. Here `bsg` bufferStrategy SunGraphics2D is used to paint to offscreen where the background is not refreshed, which does only clipping and then paints to offscreen. In order to handle the screen updated/clear the buffer, `setBackground` to component background color and `clearRect` against the clip area is used which solves the issue without causing any regression. 
> CI is green for the fix and manual test is provided.

Tejesh R has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Review updates - Test automation and updated for transparent comp
 - Merge branch 'master' of https://git.openjdk.java.net/jdk into branch_8187759
 - Review fix
 - Linux tag added
 - fix + manual test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17081/files
  - new: https://git.openjdk.org/jdk/pull/17081/files/c72d9295..67a8709e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17081&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17081&range=01-02

  Stats: 945493 lines in 8127 files changed: 264369 ins; 572704 del; 108420 mod
  Patch: https://git.openjdk.org/jdk/pull/17081.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17081/head:pull/17081

PR: https://git.openjdk.org/jdk/pull/17081