If the quote character appears in a field value, then escape
it by printing the character twice. When escaping whitespace
with the backslash character, also escape the backslash
character itself.
Add a ws_escape_csv function to wsutil and use it for tshark.
Adopt the existing static escape_string_len function so that
ws_escape_csv can use it while maintaining the same output
for the other ws_escape_ functions.
Fix#10284