[jdk21u-dev] RFR: 8328299: Convert DnDFileGroupDescriptor.html applet test to main

[Satyen Subramaniam]

Backporting JDK-8328299: Convert DnDFileGroupDescriptor.html applet test to main. Converts DnDFileGroupDescriptor test from applet structure to use main function. Ran GHA Sanity Checks. Patch is clean. Backporting for parity with Oracle.

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Commit messages:
 - Backport 75195aab497a2d23548128e03f6887283dcaa7e1

Changes: https://git.openjdk.org/jdk21u-dev/pull/2450/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2450&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328299
  Stats: 258 lines in 3 files changed: 36 ins; 188 del; 34 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2450.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2450/head:pull/2450

PR: https://git.openjdk.org/jdk21u-dev/pull/2450