[css-logical-1] Order of inheritance vs. mapping in logical properties

Example from @FremyCompany:

```
  <div style="margin-left: 10px; margin-inline-start: 20px; direction: rtl">
    <div style="margin-right: inherit; margin-inline-start: inherit; direction: ltr"></div>
  </div>
```

It's clear that `margin-right` inherits 20px from the computed `margin-right` value on the parent. What about `margin-inline-start`, though? Does it inherit 10px or 20px?