Expand anchors to full URL on server rendering

This fixes bug 72490 and any similar issues where we're doing:

[$1 text of link]

but $1 is not a fully qualified URL.

There is a bug (bug 66746) to provide i18n support so it can be done
without creating an external link (which the above does), but this
fixes the broken user experience in the meantime.

Bug: 72490
Change-Id: I615a1178be61ea911855e92a131dea980ef27554
Merge "Expand anchors to full URL on server rendering"