RFR: 8297201: Obsolete AliasLevel flag

[Tobias Hartmann]

The AliasLevel flag was deprecated in JDK 19 by [JDK-8075816](https://bugs.openjdk.org/browse/JDK-8075816) and should now be obsoleted. Patch is slightly adjusted https://github.com/openjdk/jdk/pull/8140/commits/6a1bed2d7ed5494b051fae09d28787fd01de9635, originally from @tobiasholenstein.

Thanks,
Tobias

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Commit messages:
 - Missed do_aliasing() check
 - Added sanity assert and cleanup
 - 8297201: Obsolete AliasLevel flag

Changes: https://git.openjdk.org/jdk/pull/11207/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11207&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297201
  Stats: 75 lines in 10 files changed: 2 ins; 55 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/11207.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11207/head:pull/11207

PR: https://git.openjdk.org/jdk/pull/11207