[jdk11u-dev] RFR: 8278456: Define jtreg jdk_desktop test group time-based sub-tasks for use by headful testing. [v2]

[Amos]

> - Backport for [JDK-8278456](https://bugs.openjdk.org/browse/JDK-8278456)

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

  Fix Test Case Error: group not found: jdk_accessibility
  
  Fix the test case error:
  - testdata/jtreg/jtreg_test_11/test/jdk/TEST.groups: group jdk_desktop_part1: group not found: jdk_accessibility
  
  Reason
  - https://bugs.openjdk.org/browse/JDK-8236044 added a new group jdk_accessibility
  
  Solution
  - Add a `jdk_accessibility` placeholder
  - When this change back ported later, can add the contents of https://hg.openjdk.org/jdk/jdk14/rev/66ddad9cdd9d

-------------

Changes:
  - all: https://git.openjdk.org/jdk11u-dev/pull/2164/files
  - new: https://git.openjdk.org/jdk11u-dev/pull/2164/files/26ce634f..ce3c4acb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2164&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2164&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2164.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2164/head:pull/2164

PR: https://git.openjdk.org/jdk11u-dev/pull/2164