Keep the last bits of tab title with ElideLeft

This was the behavior since commit ca61bd99 (included since version
4.4.80), but was lost in the QTabBar revamp, and then re-added with
ElideMiddle in commit d375a694.

Both ElideLeft and ElideMiddle have their merits. However, as the
QTabBar revamp aimed to preserve existing behavior as much as possible,
we restore the old behavior first.

utilities/konsole!32