Add support for ECMA-48 REP: repeating previous character

Patch by btown using lxde/qtermwidget@60221da by @yan12125

ECMA-48 8.3.103 describes the sequence CSI Pn b for repeating the
previous character in the data stream. This sequence has been present
in XTerm since January 1997 and has been added to the latest terminfo
entry for xterm-new and derived entries such as xterm-256color.

https://phabricator.kde.org/D10064