bug#35129: Unsupported escape sequences for progress in shell

[Juri Linkov]

Some escape sequences are unhandled in shell mode.
Most often they appear when running `apt install'
that shows its progress bar that is supposed to stay
on the same line, but spreads over several lines,
so the output looks like a mess (where ^[7 and ^[8
are escape sequences currently still unhandled):

  debconf: unable to initialize frontend: Dialog
  debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell 
buffer, or without a controlling terminal.)
  debconf: falling back to frontend: Readline
  ^[7Progress: [  0%] 
[................................................................................................]
 ^[8
  ^[7Progress: [  6%] 
[######..........................................................................................]
 ^[8
  ^[7Progress: [ 13%] 
[############....................................................................................]
 ^[8
  ^[7Progress: [ 19%] 
[##################..............................................................................]
 ^[8
  ^[7Progress: [ 25%] 
[########################........................................................................]
 ^[8
  ^[7Progress: [ 31%] 
[##############################..................................................................]
 ^[8
  ^[7Progress: [ 38%] 
[####################################............................................................]
 ^[8
  ^[7Progress: [ 44%] 
[##########################################......................................................]
 ^[8
  ^[7Progress: [ 50%] 
[################################################................................................]
 ^[8
  ^[7Progress: [ 56%] 
[######################################################..........................................]
 ^[8
  ^[7Progress: [ 63%] 
[############################################################....................................]
 ^[8
  ^[7Progress: [ 69%] 
[##################################################################..............................]
 ^[8
  ^[7Progress: [ 75%] 
[########################################################################........................]
 ^[8
  ^[7Progress: [ 81%] 
[##############################################################################..................]
 ^[8
  ^[7Progress: [ 88%] 
[####################################################################################............]
 ^[8
  ^[7Progress: [ 94%] 
[##########################################################################################......]
 ^[8

I'm making this report because escape sequences for colors are handled fine,
and visually these indicators have the green background.