RFR: 8350964: Add an ArtifactResolver.fetch(clazz) method [v4]

[Matthew Donovan]

> In this PR, I created a new method, `ArtifactResolver.fetchOne()`, to consolidate duplicate code across tests.

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

  updated code to remove extraneous null checks

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23989/files
  - new: https://git.openjdk.org/jdk/pull/23989/files/4791105e..c1b79738

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23989&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23989&range=02-03

  Stats: 44 lines in 6 files changed: 12 ins; 24 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/23989.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23989/head:pull/23989

PR: https://git.openjdk.org/jdk/pull/23989