RFR: 8328570: Convert closed JViewport manual applet tests to main [v2]

[Prasanta Sadhukhan]

> Few closed manual applet JViewport tests are converted to main based and opensourced

Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:

  getCOntentPane removed

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18418/files
  - new: https://git.openjdk.org/jdk/pull/18418/files/7783bf97..395730f3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18418&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18418&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18418.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18418/head:pull/18418

PR: https://git.openjdk.org/jdk/pull/18418