Simplification of @trusted

[Sönke Ludwig]

Am 18.06.2021 um 04:07 schrieb Walter Bright:
> (...)
> 
> m_core.m_handles[h] looks like it needs encapsulation in a proper 
> function that takes m_core and h as arguments.

Accessing `m_core.m_handles[h]` is `@safe`, just taking the address of 
the result is not. `scope slot = ...` might make it work in this 
particular case, but of course only with the appropriate compiler 
version and `-preview` switch.

> I got rid of a *lot* of memory management code in the back end by 
> creating a container type to do it and prevent a safe interface.

The problem here is just escaping references to contained items. At some 
point in the future, with DIP25/DIP1000 enabled by default, this will 
hopefully become a non-issue.

> Unsafe system calls like CreateFileW() can be encapsulated with a 
> wrapper that presents a safe interface.
> 
> Yes, this is extra work. But it's good work. I bet you'll like the 
> result! I sure have when I've done it.

The code that calls it *is* the `@safe` wrapper ;)  (more or less, it 
does a little bit more than that - but adding another wrapper in-between 
wouldn't really add anything apart from complexity, because the function 
is only used in a single place)