[Issue 20112] __vector casts don't do type conversions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20112

--- Comment #6 from Walter Bright <bugzilla at digitalmars.com> ---
Added a couple spec pulls to clarify:

https://github.com/dlang/dlang.org/pull/2924
https://github.com/dlang/dlang.org/pull/2925

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