RFR: 8355915: [leyden] Crash in MDO clearing the unloaded array type

[Aleksey Shipilev]

Caught this when doing benchmarks with Spring Boot. See the bug for reproducer.

The fix does similar thing to `is_excluded` and other code. When we encounter the `T[]`, we ask if its bottom component classes is not yet initialized. This fits nicely with our current uses, which skip such classes, and ever touch their (potentially nullptr) CLDs.

Additional testing:
 - [x] Ad-hoc testing with most recent spring-boot-petclinic
 - [x] Linux x86_64 server fastdebug, `runtime/cds`

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Commit messages:
 - Fix
 - Fix

Changes: https://git.openjdk.org/leyden/pull/64/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=64&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355915
  Stats: 15 lines in 1 file changed: 11 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/leyden/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/64/head:pull/64

PR: https://git.openjdk.org/leyden/pull/64