Partially add back in "support REP (repeat) escape sequence"
Add the functionality back in for xterm compatibility, but do not expose the
capability in st.info (yet).
Some notes:
It was reverted because it caused some issues with ncurses in some
configurations, namely when using BSD padding (--enable-bsdpad, BSD_TPUTS) in
ncurses it caused issues with repeating digits.
A fix has been upstreamed in ncurses since snapshot 20200523. The fix is also
backported to OpenBSD -current.