[Issue 18701] New: std.conv.emplaceRef should be made publicly available

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18701

          Issue ID: 18701
           Summary: std.conv.emplaceRef should be made publicly available
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: bootcamp, safe
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: greensunny12 at gmail.com

std.conv.emplaceRef is Phobos's internal @safe version of emplace.
Like `formattedRead`, emplace should be made @safe if no pointers are used.

Motivation:

No need for these hacks anymore - just `emplace!SafeClass(buf, 5)`

---
auto support = (() @trusted => cast(SafeClass)(buf.ptr))();
auto safeClass = emplace!SafeClass(support, 5);
---

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