Fix right-to-left tables with collapsed borders

[liZe]

Fix #2055.

Related to #2056.

[liZe]

This PR is not ready yet. #2055 is "fixed", but that’s just a workaround: border colors are wrong.

Here’s another example showing what’s left to fix:

<style>
  table {
    border-collapse:collapse;
    margin-bottom: 1em;
  }
  tr {
    border-left: 5px solid fuchsia;
    border-right: 15px solid purple;
  }
  td.right {
    background-color: yellow;
    border-bottom: 5px solid orange;
  }
  td.left {
    background-color: aqua;
    border-bottom: 15px solid teal;
  }
</style>
<table style="direction: ltr;">
  <tr>
    <td class="left">XX</td>
    <td class="right">XX XX XX</td>
  </tr>
</table>


<table style="direction: rtl;">
  <tr>
    <td class="right">XX XX XX</td>
    <td class="left">XX</td>
  </tr>
</table>