8373946: Synth ProgressBarUI implementation confuses background painting with border painting
------------- Commit messages: - Backport fe5911c7695283cb76b3d95877138b0b15bc0ba4 Changes: https://git.openjdk.org/jdk/pull/28941/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28941&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8373946 Stats: 237 lines in 3 files changed: 123 ins; 110 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/28941.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28941/head:pull/28941 PR: https://git.openjdk.org/jdk/pull/28941
