Applying Placement New to druntime and phobos

[Per Nordlöw]

On Tuesday, 4 March 2025 at 01:27:29 UTC, Manu wrote:
> Please do contribute to this effort if you're enthusiastic! I 
> have very
> little free time rn.

Tried converting a couple of usages of `emplace` and 
`moveEmplace` in a repo of mine and discovered that I'm missing a 
way to express

`moveEmplace(x, y)`

as

`new(y) typeof(y)(__rvalue(x))`

. This doesn't always work eventough `y` being assignable from 
`x`.