RFR: 8366474: Rename MetaspaceObj::is_shared() to MetaspaceObj::in_aot_cache()

[Ioi Lam]

Rename `is_shared()` in `Metaspace` (and various other classes) to `in_aot_cache()` to reflect its true meaning:
- tests if an object is inside the AOT cache's metaspace region.

Also various forms of  "shared metaspace" are updated to "aot metaspace"

Please start your review with allocations.hpp

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Commit messages:
 - 8366474: Rename MetaspaceObj::is_shared() to MetaspaceObj::in_aot_cache()

Changes: https://git.openjdk.org/jdk/pull/27016/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27016&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366474
  Stats: 199 lines in 56 files changed: 3 ins; 0 del; 196 mod
  Patch: https://git.openjdk.org/jdk/pull/27016.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27016/head:pull/27016

PR: https://git.openjdk.org/jdk/pull/27016