[jdk21u-dev] RFR: 8328673: Convert closed text/html/CSS manual applet test to main

[Goetz Lindenmaier]

I backport this test change as it also goes to 21.0.9-oracle

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Commit messages:
 - Backport cd534f8197341fbe3b3811f5be43c88090e16366

Changes: https://git.openjdk.org/jdk21u-dev/pull/1783/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1783&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328673
  Stats: 161 lines in 2 files changed: 161 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1783.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1783/head:pull/1783

PR: https://git.openjdk.org/jdk21u-dev/pull/1783