[jdk17u-dev] RFR: 8285452: Add a new test library API to replace a file content using FileUtils.java

[Goetz Lindenmaier]

I backport this for parity with 17.0.12-oracle.

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Commit messages:
 - Backport 0462d5a25258458ec7f40d76b9d910ee529f3647

Changes: https://git.openjdk.org/jdk17u-dev/pull/2295/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2295&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8285452
  Stats: 163 lines in 2 files changed: 162 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2295.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2295/head:pull/2295

PR: https://git.openjdk.org/jdk17u-dev/pull/2295