RFR: JDK-8309574: Improve core reflection tests for JEP 445

[Joe Darcy]

Add some basic core reflections tests for unnamed classes.

-------------

Commit messages:
 - JDK-8309574: Improve core reflection tests for JEP 445

Changes: https://git.openjdk.org/jdk/pull/14345/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14345&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309574
  Stats: 99 lines in 2 files changed: 95 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14345.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14345/head:pull/14345

PR: https://git.openjdk.org/jdk/pull/14345