[Issue 22509] Document implicit conversion to immutable for pure factory functions

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22509

timon.gehr at gmx.ch changed:

           What    |Removed                     |Added
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            Summary|Invalid implicit conversion |Document implicit
                   |from int* to                |conversion to immutable for
                   |immutable(int*)             |pure factory functions

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