[jdk26u] RFR: 8375231: Refactor util/ServiceLoader tests to use JUnit

[Shivangi Gupta]

Straight Backport.Tests passed

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Commit messages:
 - Backport 34705a77f9a90da5ab2a440c11d79aef7bb3ba54

Changes: https://git.openjdk.org/jdk26u/pull/62/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk26u&pr=62&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375231
  Stats: 357 lines in 11 files changed: 81 ins; 53 del; 223 mod
  Patch: https://git.openjdk.org/jdk26u/pull/62.diff
  Fetch: git fetch https://git.openjdk.org/jdk26u.git pull/62/head:pull/62

PR: https://git.openjdk.org/jdk26u/pull/62