RFR: 8328261: public lookup fails with IllegalAccessException when used while module system is being initialized

[Mandy Chung]

A simple fix.   This is caused by a bug in `VerifyAccess::isClassAccessible` that checks if a class is exported from `java.base` before the exports are fully setup.    It should check if the module system is fully initialized before checking the module exports instead.

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Commit messages:
 - 8328261: public lookup fails with IllegalAccessException when used while module system is being initialized

Changes: https://git.openjdk.org/jdk/pull/18356/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18356&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328261
  Stats: 9 lines in 1 file changed: 1 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18356.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18356/head:pull/18356

PR: https://git.openjdk.org/jdk/pull/18356