RFR: 8187759: Background not refreshed when painting over a transparent JFrame [v4]

[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 incrementally with one additional commit since the last revision:

  Frame dispose moved into EDT

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17081/files
  - new: https://git.openjdk.org/jdk/pull/17081/files/67a8709e..262ba9df

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17081&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17081&range=02-03

  Stats: 8 lines in 1 file changed: 2 ins; 0 del; 6 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