Re-work of arrays meta-data

[fparain]

Since the removal of Q-types and the notion that nullability was not part of the Java type, there was an awkward situation because nullable arrays of value types and null free arrays of value types had each a different Java mirror when they were in fact supposed to have the same Java type.
In order to accommodate to the new situation, that arrays can have properties (nullability, flatness, atomicity, etc.) that are not part of their Java type, the 1-1 relationship between the *ArrayKlass and the Java mirror must be broken.
The proposed solution is to dedicate one instance of ObjArrayKlass to represent the Java type of the array in the JVM, and have this instance being the counterpart of the Java mirror of the array, and have several instances of RefArrayKlass and FlatArrayKlass that represent the refinements of the Java array type. Each RefArrayKlass/FlatArrayKlass encodes the characteristic of a Java array for a given element type and a set of properties.

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Progress

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Reviewing

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[bridgekeeper]

👋 Welcome back fparain! A progress list of the required criteria for merging this PR into lworld will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[coleenp]

Makes sense - found a typo. Are you going to check this in with UseNewCode2 or you could add a global flag for this because I think you're going to need a new one?

[coleenp]

you have an extra j in this.

[coleenp]

The stars go with the types, ie ClassLoaderData* loader_data.

[openjdk]

@fparain this pull request can not be integrated into lworld due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout array_klasses
git fetch https://git.openjdk.org/valhalla.git lworld
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge lworld"
git push

[bridgekeeper]

@fparain This pull request has been inactive for more than 8 weeks and will be automatically closed if another 8 weeks passes without any activity. To avoid this, simply issue a /touch or /keepalive command to the pull request. Feel free to ask for assistance if you need help with progressing this pull request towards integration!

[fparain]

/keepalive

[openjdk]

@fparain The pull request is being re-evaluated and the inactivity timeout has been reset.

[openjdk]

⚠️ @fparain This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).