Fix handling of terminal escape sequences in TUI

Fix handling of terminal escape sequences in TUI

A user noticed that if the remote sends terminal escape sequences from
the "monitor" command, then these will not be correctly displayed when
in TUI mode.

I tracked this down to remote.c emitting one character at a time --
something the TUI output functions did not handle correctly.

I decided in the end to fix in this in the ui-file layer, because the
same bug seems to affect logging and, as is evidenced by the test case
in this patch, Python output in TUI mode.

The idea is simple: buffer escape sequences until they are either
complete or cannot possibly be recognized by gdb.

Regression tested on x86-64 Fedora 40.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=14126
Approved-By: Andrew Burgess <aburgess@redhat.com>