RFR: 8342988: GHA: Build JTReg in single step

[Aleksey Shipilev]

It is visible in current GHA runs that building jtreg in all worker at once sometimes break on dependencies checkout, for example:


[build.sh][INFO] CYGWIN_OR_MSYS=0
[build.sh][INFO] JAVA_HOME: /usr/lib/jvm/temurin-17-jdk-amd64
[build.sh][INFO] Downloading https://archive.apache.org/dist/ant/binaries/apache-ant-1.10.8-bin.zip to /home/runner/work/jdk/jdk/jtreg/src/make/../build/deps/apache-ant-1.10.8-bin.zip
Error: sh][ERROR] wget exited with exit code 4
Error: Process completed with exit code 1.


I suppose this is a side-effect of pulling lots of dependencies all at once. Building jtreg on every platform exposes us to these issues more often. Additionally, we had problems with building jtreg on various platforms. 

We do not have to build jtreg for every platform. We can just have a job step that does it once, and stores it in the cache for all dependent jobs to use. It would also save some build time across various jobs.

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Commit messages:
 - Fix
 - Rename select -> prepare
 - Fix

Changes: https://git.openjdk.org/jdk/pull/21692/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21692&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342988
  Stats: 65 lines in 6 files changed: 28 ins; 7 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/21692.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21692/head:pull/21692

PR: https://git.openjdk.org/jdk/pull/21692