RFR: 8341483: Clarify special case handling of Types.getArrayType

[Joe Darcy]

Add specification and tests for invalid inputs to getArrayType that generation an exception. As initially written, this PR changes the behavior on NONE and the null type.

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Commit messages:
 - JDK-8341483: Clarify special case handling of Types.getArrayType

Changes: https://git.openjdk.org/jdk/pull/21346/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21346&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341483
  Stats: 64 lines in 3 files changed: 52 ins; 0 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/21346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21346/head:pull/21346

PR: https://git.openjdk.org/jdk/pull/21346