RFR: 8341587: [premain] Support Soft/Weak Reference in AOT cache

[Mat Carter]

Add support to the AOT cache for References (soft, weak and phantom)
Remove the workarounds that were added because References weren't supported

Confirmed from logs that References are stored in the cache correctly

All demos run successfully on osx

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Commit messages:
 - Addressing PR feedback - moving assert higher
 - Fix missing line at end of file
 - Remove superfluous SuppressWarnings now we've removed unchecked casts
 - Remove workarounds now that References are supported in CDS

Changes: https://git.openjdk.org/leyden/pull/41/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=41&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341587
  Stats: 114 lines in 9 files changed: 9 ins; 100 del; 5 mod
  Patch: https://git.openjdk.org/leyden/pull/41.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/41/head:pull/41

PR: https://git.openjdk.org/leyden/pull/41