Only quote CSV string values if necessary

[into-the-v0id]

Currently all string values are quoted when using the CSV formatter:

$ echo '["hello", "world", "hello,world"]' | jq -r '@csv'
"hello","world","hello,world"

This PR changes that to only quote string values when actually needed:

$ echo '["hello", "world", "hello,world"]' | jq -r '@csv'
hello,world,"hello,world"

Here is a more extensive example:

$ echo '[0, null, true, "hello", "hello,world", "a\"b", "one\ntwo", "foo, \"bar\nbaz\" end"]' | jq -r '@csv'
0,,true,hello,"hello,world","a""b","one
two","foo, ""bar
baz"" end"