[jdk21u-dev] RFR: 8328570: Convert closed JViewport manual applet tests to main

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle

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Commit messages:
 - Backport 725d87bbc2abae2ca856d91668f0a494f93fca1c

Changes: https://git.openjdk.org/jdk21u-dev/pull/2067/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2067&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328570
  Stats: 428 lines in 5 files changed: 428 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2067.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2067/head:pull/2067

PR: https://git.openjdk.org/jdk21u-dev/pull/2067