[jdk21u-dev] RFR: 8328225: Convert ImageDecoratedDnD.html applet test to main

[Goetz Lindenmaier]

I backport this for parity with 21.0.9-oracle.

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Commit messages:
 - Backport a112fc8bac8ddee87c8555b156519a2785d3223b

Changes: https://git.openjdk.org/jdk21u-dev/pull/2057/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2057&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328225
  Stats: 254 lines in 2 files changed: 52 ins; 185 del; 17 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2057.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2057/head:pull/2057

PR: https://git.openjdk.org/jdk21u-dev/pull/2057