RFR: JDK-8297215: Update libs tests to use @enablePreview [v2]

[Joe Darcy]

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

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11222/files
  - new: https://git.openjdk.org/jdk/pull/11222/files/88a566c6..f3fc9e26

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11222&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11222&range=00-01

  Stats: 3 lines in 2 files changed: 0 ins; 2 del; 1 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