border-style should support -x, -y, -l, -r, -t, and -b modifiers

[ShawnTheBeachy]

In the same way we can do border-l-2, we should be able to do border-l-dashed to allow for mixed border styles. I believe it would look something like this:

.border-y-dashed {
    border-bottom-style: dashed;
    border-top-style: dashed;
}

.border-x-dashed {
    border-left-style: dashed;
    border-right-style: dashed;
}

.border-l-dashed {
    border-left-style: dashed;
}

.border-r-dashed {
    border-right-style: dashed;
}

.border-t-dashed {
    border-top-style: dashed;
}

.border-b-dashed {
    border-bottom-style: dashed;
}