fix issue 16597 - deprecate shared as associative array storage class

[ghost]

It's not possible to output directly an error because in theory it would be possible that someone uses a shared AA in combination with synchronization barriers, so instead encourage using __gshared.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	16597	major	Initializing a shared hashmap segfaults

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#9366"

[jacob-carlborg]

Is this in the spec?

[ghost]

Not to my knowledge. To be perfectly honest, this PR is naively motivated by a comment in the issue.
The idea is just to avoid head scratching for the people trying to do something that cant work.

[PetarKirov]

We should probably also disallow shared(V)[K], as I don't think the AA implementation takes any precautions to guard reads/writes of shared values. Can you add a test for this as well?

[ghost]

Sorry i don't feel it anymore. I keep the branch if some one wants to polish and is more convinced about the validity of this restriction.