`AlertCustomOptions` doesn't work properly

[Byloth]

Make it work!

vuert/packages/core/src/types/alert/index.ts

Line 6 in 32853b0

export interface AlertCustomOptions { }

[Byloth]

import type { IconDefinition } from "@fortawesome/free-brands-svg-icons";

declare module "@byloth/vuert"
{
    interface AlertCustomOptions
    {
        icon?: IconDefinition;
    }
}

The previous definition doesn't work correctly.
It ends up breaking 2 different things:

1. The icon key is now defined as string & IconDefinition which makes using both the string or IconDefinition types impractical.
2. Any other symbols exported from @byloth/vuert end up not being exported at all; the only valid key exported is actually the AlertCustomOptions interface.

Solve these problems.