RFR: 8375231: Refactor util/ServiceLoader tests to use JUnit [v2]

[Justin Lu]

> This PR converts the TestNG tests in _util/ServiceLoader_ (7), _util/StringJoiner_ (3), and _util/Vector_ (1) to JUnit.
> The first commit is from the automated tool, the rest are manual changes done after.
> 
> Before
> ServiceLoader: Framework-based tests: 62 = 62 TestNG + 0 JUnit
> StringJoiner: Framework-based tests: 32 = 32 TestNG + 0 JUnit
> Vector: Framework-based tests: 9 = 9 TestNG + 0 JUnit
> 
> After
> ServiceLoader: Framework-based tests: 62 = 0 TestNG + 62 JUnit
> StringJoiner: Framework-based tests: 32 = 0 TestNG + 32 JUnit
> Vector: Framework-based tests: 9 = 0 TestNG + 9 JUnit

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

  Retain the removed whitespace in BadProvidersTest.java

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/29210/files
  - new: https://git.openjdk.org/jdk/pull/29210/files/e717570a..dedfc033

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29210&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29210&range=00-01

  Stats: 6 lines in 1 file changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/29210.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29210/head:pull/29210

PR: https://git.openjdk.org/jdk/pull/29210