RFR: JDK-8297215: Update libs tests to use @enablePreview

[Joe Darcy]

Similar to an update recently done for langtools tests, update the libraries regression tests to take advantage of the @enablePreview jtreg feature.

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Commit messages:
 - JDK-8297215: Update libs tests to use @enablePreview

Changes: https://git.openjdk.org/jdk/pull/11222/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11222&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297215
  Stats: 122 lines in 36 files changed: 33 ins; 1 del; 88 mod
  Patch: https://git.openjdk.org/jdk/pull/11222.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11222/head:pull/11222

PR: https://git.openjdk.org/jdk/pull/11222