[Issue 21603] Provide deprecation warning or error for placement new syntax

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21603

--- Comment #1 from Kyle <kbcomm at protonmail.com> ---
DMD 2.098.0 removes class allocators from the language -
https://dlang.org/changelog/2.098.0.html#remove_alloc

Placement new syntax still triggers a "no allocator for 'CLASSNAME'" error. As
far as I know there's no way to use placement new syntax without an allocator,
so this should also be removed. I think it's worth noting that Andrei's book
tells people they can use this syntax so a deprecation notice would be helpful.

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