[jdk21u-dev] RFR: 8323515: Create test alias "all" for all test roots

[Aleksey Shipilev]

Improves JDK testability by allowing to run all tests easily.

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Commit messages:
 - Backport 2d5cb97288f7bf5acaa24632118d6a7a6a53c93e
 - Backport 8b9bf758801400e4491326cd4c90fc117b9d97e1

Changes: https://git.openjdk.org/jdk21u-dev/pull/256/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=256&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323515
  Stats: 50 lines in 5 files changed: 42 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/256.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/256/head:pull/256

PR: https://git.openjdk.org/jdk21u-dev/pull/256