Support or override rollup ouput config `sanitizeFileName`

Add the ability to override `sanitizeFileName` in [rollup outputConfig](https://github.com/egoist/tsup/blob/9b813620a884f5b780346a240c51ead321227bce/src/rollup.ts#L201).
By default, characters like `+` are replaced with `_`, thus generating differences between artifacts names in the following case:

```ts
import { defineConfig } from 'tsup';

export default defineConfig([
{
entry: ['./+config.h.ts'],
format: ['esm'],
dts: {
entry: ['./+config.h.ts'],
},
},
]);
```

It currently generates the following files:

```
- /dist/+config.h.js
- /dist/_config.h.d.ts <--
```

With `sanitizeFileName: false`, the file names would be more correct and predictable:
```
- /dist/+config.h.js
- /dist/+config.h.d.ts <--
```