sokol-d: Static Struct

[Matheus Catarino]

Hi everyone. 👋


Currently I'm working on D binding for sokol project (truly a 
dual bindgen [sokol-tools, sokol-header]) which could be merged 
into the upstream project.


Up to now, my "ideal" configuration has been to run all the 
ported examples (from other supported bindings) on Drt or betterC 
provided @safe has DIP1000 enabled (not obligatory).


Except for the "clear" example (no have structs) works, the rest 
of the examples have partial execution, without 2D/3D animations, 
like the original ported examples.

e.g.:
https://github.com/kassane/sokol-d/blob/main/src/examples/sgl_context.d

Based on the articles in the official documentation, I tried to 
use `__gshared` (no `@safe`) to attribute both the display and 
offscreen structures inside state, but it didn't work.
```d
@disable struct State
{
     @disable this();
     @disable this(this);
     __gshared Display display;
     __gshared Offscreen offscreen;
}
static assert(!__traits(isDisabled, State));
static assert(!__traits(isCopyable, State));
```

## Reproduce

![sokol_d_sglcontext](https://github.com/kassane/sokol-d/assets/6756180/0e8391f6-056e-46db-b8e8-021309954ffe)

## Expected

![sokol_zig_sglcontext](https://github.com/kassane/sokol-d/assets/6756180/576176f8-005a-408d-9ae7-00948161b19f)