* If the leftmost tab is selected, scroll all the way to the left
* If the rightmost tab is selected, scroll all the way to the right
* If a tab in the middle is selected, scroll to center it
* If the selected tab is wider than the tab container, make sure its
start (left edge in LTR, right edge in RTL) is always made visible.
As Bartosz reminded me, .scrollLeft in RTL is a cross-browser nightmare
(see https://github.com/othree/jquery.rtl-scroll-type), so add a bunch
of code working around this. Some of this logic is in OOUI already, but
what's there is not enough for what we need here, and we also don't want
to load OOUI for this.
Bug: T223142
Change-Id: Ica298954b42f9daa4819043ec24bc0266290a927
