RFR: 7903943: Release jtreg 7.5.1

Tue Feb 4 09:50:07 UTC 2025

Please review this change preparing the `7.5.1` release of `jtreg`.

The version number `7.6` will be restored on the main branch after the release; a dedidated `7.5.x` branch was not required, yet.

This change also updates the `CHANGELOG.md` file with noteworthy items. It also removes the detailed description of the now removed `LIBRARY.properties` support from the `7.5` section.

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Commit messages:
 - 7903943: Release jtreg 7.5.1

Changes: https://git.openjdk.org/jtreg/pull/245/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=245&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903943
  Stats: 15 lines in 2 files changed: 9 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/jtreg/pull/245.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/245/head:pull/245

PR: https://git.openjdk.org/jtreg/pull/245