Improve rendering Markdown lists in a terminal (#60519)
This changes how Markdown lists are rendered in the Terminal:
- the list is no longer indented by two spaces
- the bullet points are now followed by a single space, not two
- extra lines in an entry are indented correctly across all levels
- fix printing / indentation for ordered lists starting at an index
other than 1: the padding for the labels was being computed incorrectly
- fix word wrap with a given column limit
Consider this Markdown input:
```md
Before the list:
- top level\
with an extra line
- second level\
again with an extra line
- third level\
yet again with an extra line
- fourth level\
and another extra line
- fifth level\
final extra line
- back to top level
```
Then with Julia master it renders in the terminal like this:
```
Before the list:
• top level
with an extra line
– second level
again with an extra line
▪ third level
yet again with an extra line
– fourth level
and another extra line
▪ fifth level
final extra line
• back to top level
```
With this PR:
```
Before the list:
• top level
with an extra line
– second level
again with an extra line
▪ third level
yet again with an extra line
– fourth level
and another extra line
▪ fifth level
final extra line
• back to top level
```
