[jdk17u-dev] RFR: 8278456: Define jtreg jdk_desktop test group time-based sub-tasks for use by headful testing.

[Goetz Lindenmaier]

I backport this for parity with 17.0.8-oracle.

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Commit messages:
 - Backport 81c56c700a47c7f1b7855052de17eb88fac84674

Changes: https://git.openjdk.org/jdk17u-dev/pull/1453/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1453&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278456
  Stats: 23 lines in 1 file changed: 17 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1453.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1453/head:pull/1453

PR: https://git.openjdk.org/jdk17u-dev/pull/1453