[jdk17u-dev] RFR: 8296718: Refactor bootstrap Test Common Functionalities to test/lib/Utils

[Goetz Lindenmaier]

I backport this for parity with 17.0.14-oracle.

Applies clean, but FILE_SEPERATOR was already backported to Utils.java.
Second commit removes redundant definition.

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Commit messages:
 - Resolve FILE_SEPARATOR in Utlis.java
 - Backport cc8bf95046d1fba0f88b0e17481f36b2be870659

Changes: https://git.openjdk.org/jdk17u-dev/pull/3050/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3050&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296718
  Stats: 468 lines in 4 files changed: 231 ins; 234 del; 3 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3050.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3050/head:pull/3050

PR: https://git.openjdk.org/jdk17u-dev/pull/3050