fix markdown list rendering

[KristofferC]

Fixes #37232
Fixes JuliaDebug/Debugger.jl#287

Before, the wrapped_lines put things on different lines onto the same line:

julia> using Markdown

julia> md = @md_str """
       Misc:\\
       - `o`: open the current line in an editor\\
       """;

julia> str = sprint(io->Markdown.terminline(io, md.content[end].content))
"Misc:\n- o: open the current line in an editor\n"

julia> Markdown.wrapped_lines(stdout, str)
1-element Vector{AbstractString}:
 "Misc: - o: open the current line in an editor"

Now:

2-element Vector{String}:
 "Misc:"
 "- o: open the current line in an editor"