RFR: 7904000: Update to build with JDK 17

Mon May 19 19:48:40 UTC 2025

Please review this change to update to build of `jtreg` with JDK 17.

Note that we still keep the `--release 8` for agent classes, and `--release 11` for tool classes as-is. That means, the runtime required to launch `jtreg` is unchanged.
Note also, that some tests may require (bundled) external libraries, such as AsmTools 8.1, which moved to Java 17 as their baseline.

This change also sets the version of `jtreg` to `7.6`, the next release number.

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Commit messages:
 - 7904000: Update to build with JDK 17

Changes: https://git.openjdk.org/jtreg/pull/264/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=264&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7904000
  Stats: 8 lines in 5 files changed: 1 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jtreg/pull/264.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/264/head:pull/264

PR: https://git.openjdk.org/jtreg/pull/264