text: Title: [REQUEST] Add support for 3-digits HEX colors
  Body: Consider posting in https://github.com/textualize/rich/discussions for feedback before raising a feature request.
  
  > Have you checked the issues for a similar suggestions?
  
  Yes
  
  > **How would you improve Rich?**
  
  Adding support for 3 digit colors.
  
  > Give as much detail as you can. Example code of how you would like it to work would help.
  <img src="https://github.com/Textualize/rich/assets/30776937/35f5b20c-59a0-4bc7-92b4-ac4dca7da735" width=37.5%>
  
  ---
  
  > **What problem does it solve for you?**
  
  Writing all the letters. 🙂
  
  > What problem do you have that this feature would solve? I may be able to suggest an existing way of solving it.
  
  If color contains 3 digits, repeat each letter, thus expanding the color code.
  ```py
  def color_expand(color: str) -> str:
      if color.startswith("#"):
              if len(color) == 4: # "#xyz"
                      return "#{0}".format("".join(c * 2 for c in list(color)[1:])) # skip "#"
              else:
                      return color
      else:
              return color
  ```