Edit and Edit source tab were reversed in RTL in the Vector integration

If we're in RTL mode and the skin is Vector-based, we need to reverse
the order of the tabs in the DOM, because that's a weird thing that
Vector does to render tabs in RTL.

See https://bugzilla.wikimedia.org/show_bug.cgi?id=46947 for discussion
about the Vector behavior.

Bug: 48017
Change-Id: Ie1214b08450aefed893739a2b862cb1e9b23a2ef
Merge "Edit and Edit source tab were reversed in RTL in the Vector integration"