Proposed changes to `bindings --pkg-name`

I think that the `bindings --pkg-name` option should automatically create `imports` and `exports` folders. This would mean that we could also remove the `bindings --export-pkg-name` option. I think this would offer more clarity and less friction. This will require edits to both `wit-bindgen-go` and `componentize-go`.

Just in case the above isn't clear:

Current:
```
$ mkdir -p internal/exports
$ componentize-go \
bindings \
--output internal/imports \
--pkg-name internal/imports \
--export-pkg-name internal/exports
$ mv internal/imports/wit_exports imports/exports
$ ls internal
exports imports
```

Proposed:
```
$ componentize-go bindings --output internal --pkg-name internal
$ ls internal
exports imports

```

@dicej Any thoughts/concerns?