Support generation of hls-stan-plugin diagnostics without fancy characters like '✲'

## Is your enhancement request related to a problem? Please describe.

Diagnostics from the stan plugin use a character which my terminal (WSL) does not support, so the diagnostic looks rather ugly


Note the tiny rectangle indicating that the character cannot be displayed. A terminal that supports this character (windows terminal) displays the diagnostic like this


Note that this terminal displays a fancy asterisk.

## Describe the solution you'd like

Obviously ideally my terminal would support these fancy characters, but it does not, and I'm sure others don't as well. So I think a reasonable way to help users of such terminals would be to provide a way for hls-stan-plugin diagnostics to be generated using a non-fancy asterisk, `*`, or any suitable replacement that is more commonly supported.

## Describe alternatives you've considered

I have considered switching terminals, but Windows Terminal has larger problems for me right now, and WSL is the best terminal for my use-case at the moment. Additionally, me switching terminals doesn't solve this for others who might be in the same situation.