RFR: 8299553: Make ScaledEtchedBorderTest.java comprehensive [v2]

[Alexey Ivanov]

> The `ScaledEtchedBorderTest.java` test ([JDK-8279614](https://bugs.openjdk.org/browse/JDK-8279614)) verifies that the thickness of lines of `EtchedBorder` is consistent. The component inside had the same background color as the frame. Yet if there's another component the background of which is different, that background could be seen.
> 
> The updated test covers the scenario reported in [JDK-8294921](https://bugs.openjdk.org/browse/JDK-8294921).
> 
> The bug itself is fixed by refactoring [JDK-8294680](https://bugs.openjdk.org/browse/JDK-8294680) the border rendering code which uses a more precise coordinate calculation, see #11571. Thus, I contribute the test under a separate bugid.
> 
> I also modified `ScaledLineBorderTest.java` so that the location of the child panels is saved when they're created as done in `ScaledTextFieldBorderTest.java` in #11498. I removed the unused `Component` import after this modification from both tests.

Alexey Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  Move State enum before checkBorder where it's used

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11836/files
  - new: https://git.openjdk.org/jdk/pull/11836/files/b78389e8..f7783e43

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11836&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11836&range=00-01

  Stats: 22 lines in 2 files changed: 11 ins; 11 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11836.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11836/head:pull/11836

PR: https://git.openjdk.org/jdk/pull/11836