RFR: 8366474: Rename MetaspaceObj::is_shared() to MetaspaceObj::in_aot_cache() [v3]

[Ioi Lam]

> This PR is one (of many) steps in [JDK-8366473](https://bugs.openjdk.org/browse/JDK-8366473) (Refactor CDS source code with new AOT terminology):
> 
> 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

Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Also renamed ConstantPool::is_shared() because it shadows MetaspaceObj::is_shared()
 - Merge branch 'master' into 8366474-rename_metaspaceobj_is_shared_to_in_aot_cache
 - Removed MetaspaceShared -> AOTMetaspace changes that are intended for https://github.com/openjdk/jdk/pull/27017
 - 8366474: Rename MetaspaceObj::is_shared() to MetaspaceObj::in_aot_cache()

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Changes: https://git.openjdk.org/jdk/pull/27016/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27016&range=02
  Stats: 204 lines in 55 files changed: 3 ins; 0 del; 201 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