Movement against float.init being nan

[Nick Treleaven]

On Saturday, 20 August 2022 at 03:12:43 UTC, Steven Schveighoffer 
wrote:
> You can't even `assert(x != double.init)`. You have to use an 
> esoteric function `isNaN` for that.

Actually, you can use `is`:
```d
static assert(float() is float.nan);
```
 From the spec:

> For struct objects and floating point values, identity is 
> defined as the bits in the operands being identical.

I'm making a pull to add a spec example so it's more obvious.