text: Title: Support library keywords with both embedded and normal arguments
  Body: In https://github.com/robotframework/robotframework/issues/4234 / https://github.com/robotframework/robotframework/pull/4319 support for user keywords with embedded and normal arguments was added. 
  
  It would be useful if we could do the same for library keywords in the same manor e.g.
  
  ```python
  @keyword('Number of ${animals} should be') 
  def example(animals, count):
      ...
  ```
  
  ```
  Number of horses should be    2
  Number of horses should be    count=2
  Number of dogs should be    3
  