Export type `Level` to externally work with levels that are passed to the `setHeading` and `toggleHeading` commands, instead of only being able to pass literal numbers.
Example:
```
// where `selectedHeadingLevel` changes as part of other logic
this.editor.commands.toggleHeading({ level: this.selectedHeadingLevel })
```
Co-authored-by: Britta Weiland <weiland@bryter.io>