ui/console-vc: introduce parsing of the 'ESC ( <ch>' sequence

ui/console-vc: introduce parsing of the 'ESC ( <ch>' sequence

This change introduces parsing of the 'ESC ( <ch>' sequence, which is
supposed to change character set [1]. In the QEMU case, the
introduced parsing logic does not actually change the character set, but
simply parses the sequence and does not let output of a tool to be
corrupted with leftovers: `top` sends 'ESC ( B', so if character
sequence is not parsed correctly, chracter 'B' appears in the output:

  Btop - 11:08:42 up 5 min,  1 user,  load average: 0BB
  Tasks:B 158 Btotal,B  1 Brunning,B 157 Bsleeping,B   0 BsBB
  %Cpu(s):B  0.0 Bus,B  0.0 Bsy,B  0.0 Bni,B 99.8 Bid,B  0.2 BB
  MiB Mem :B   7955.6 Btotal,B   7778.6 Bfree,B     79.6 BB
  MiB Swap:B      0.0 Btotal,B      0.0 Bfree,B      0.0 BB

      PID USER      PR  NI    VIRT    RES    SHR S B
  B    735 root      20   0    9328   3540   3152 R B
  B      1 root      20   0   20084  10904   8404 S B
  B      2 root      20   0       0      0      0 S B

[1] https://vt100.net/docs/vt100-ug/chapter3.html#SCS

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20250226075913.353676-2-r.peniaev@gmail.com>