RFR: JDK-8015739: Background of JInternalFrame is located out of JInternalFrame

[Harshitha Onkar]

JInternalFrame background color seems to overflow into the border region. This issue is more prominently seen on Windows - Metal LAF (with fractional scaling, as show below). The primary reason is border scaling issue as observed in  - [JDK-8279614](https://bugs.openjdk.org/browse/JDK-8279614) & [JDK-8282958](https://bugs.openjdk.org/browse/JDK-8282958)

The fix involves a similar approach as described here https://github.com/openjdk/jdk/pull/7449#issuecomment-1068218648. The test checks the midpoint and corners of borders to check if the internal frame's background color is located out of JInternalFrame.

![image](https://user-images.githubusercontent.com/95945681/190233555-a7e00f2c-9003-4c11-84fb-207957838c2f.png)

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Commit messages:
 - added test summary
 - updated test case
 - Added test case, minor position changes to shadow lines
 - expanded imports
 - JIF Metal Border Scaling - Initial changes

Changes: https://git.openjdk.org/jdk/pull/10274/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10274&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8015739
  Stats: 402 lines in 2 files changed: 354 ins; 5 del; 43 mod
  Patch: https://git.openjdk.org/jdk/pull/10274.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10274/head:pull/10274

PR: https://git.openjdk.org/jdk/pull/10274