Graph does not support multiple imports of the same specifier

When doing something like this:

```js
import a from "./a.js";
import * as b from "./a.js";
const c = await import("./a.js");
```

The dependencies for the module only include one import site. They should actually be two seperate dependency objects, as they "may" differ in ways (like import assertions or type definitions).

That being said, it still works and adding support for it would make everything related to it fairly complex, as knowing the import location would become essential for accessing information (unless we stored a vec of locations, and associated information, like it being a dynamic import and any import assertions).