vt: add support for smput/rmput escape codes

Support "\e[?1049h" and "\e[?1049l" escape codes.
This patch allows programs to enter and leave alternate screens.
This feature is widely available in graphical terminal emulators and mostly
used by fullscreen terminal-based user interfaces such as text editors.
Most editors such as vim and nano assume this escape code in not supported
and will not try to print the escape sequence if TERM=linux.
To try out this patch, run `TERM=xterm-256color vim` inside a VT.

Signed-off-by: Calixte Pernot <calixte.pernot@grenoble-inp.org>
Link: https://lore.kernel.org/r/20250825125607.2478-3-calixte.pernot@grenoble-inp.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>