RFR: 8139173: [macosx] JInternalFrame shadow is not properly drawn

[Toshio Nakamura]

JInternalFrame's bottom area is not properly drawn with Aqua LAF.
This problem remained for long time, but we recognized it recently.

According to the bug report, it depends on MacOS's version. I don't have old ones (10.10 and 10.11 in the report), but the current MacOS can recreate the issue. I confirmed the following OS versions recreated this issue and this patch could solve it.

Mojave 10.14.6
Catalina 10.15.7
Big Sur 11.6.2
Monterey 12.1

jtreg "javax/swing" and "java/awt" have no regression.

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Commit messages:
 - 8139173: [macosx] JInternalFrame shadow is not properly drawn

Changes: https://git.openjdk.java.net/jdk/pull/7228/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7228&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8139173
  Stats: 141 lines in 2 files changed: 138 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7228.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7228/head:pull/7228

PR: https://git.openjdk.java.net/jdk/pull/7228