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.

st.info

@@ -184,6 +184,8 @@ st-mono| simpleterm monocolor,
 # XTerm extensions
 	rmxx=\E[29m,
 	smxx=\E[9m,
+# disabled rep for now: causes some issues with older ncurses versions.
+#	rep=%p1%c\E[%p2%{1}%-%db,
 # tmux extensions, see TERMINFO EXTENSIONS in tmux(1)
 	Tc,
 	Ms=\E]52;%p1%s;%p2%s\007,