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

[Sergey Bylokhov]

On Mon, 12 Feb 2024 05:38:17 GMT, Tejesh R <tr at openjdk.org> wrote:

>> 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

Marked as reviewed by serb (Reviewer).

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

PR Review: https://git.openjdk.org/jdk/pull/17081#pullrequestreview-1889509957