[Feature]: The Splitter component supports pixel size

### Describe the feature

Currently, the `min-size`, `default-size`, and `max-size` properties of the Splitter component only support percentages. Sometimes I wish to set them in pixels.

Example:
``` vue
<SplitterPanel
    min-size="35px"
>
```

### Additional information

- [ ] I intend to submit a PR for this feature.
- [ ] I have already implemented and/or tested this feature.