patch 9.0.2069: possible to escape bracketed paste mode with Ctrl-C

patch 9.0.2069: possible to escape bracketed paste mode with Ctrl-C

Problem:  possible to escape bracketed paste mode with Ctrl-C
Solution: Do not handle Ctrl-C specially when key_protocol
          is in use, makes bracketed paste mode more robust

When a key protocol is in use Ctrl-C will be sent as an escape sequence,
but a raw Ctrl-C can be sent when pasting data. Pass this through, so
that a Ctrl-C can be pasted and won't result in exiting insert mode
(where the rest of the pasted keys can cause all kind of nasty
side-effects).

Many terminals will strip control characters in paste data (and xterm
will strip ^C since version 388), but this provides some defense in
depth if users change settings like xterm's allowPasteControls.

closes: #13398

Signed-off-by: David Leadbeater <dgl@dgl.cx>
Signed-off-by: Christian Brabandt <cb@256bit.org>