Disable bracketed paste in a terminal in char mode

Disable bracketed paste in a terminal in char mode

In char mode, a terminal doesn't accept bracketed paste events,
therefore we should disable them; see Bug#24639.  To decouple the XTerm
management from term.el, introduce a per-buffer setting to disable
bracketed paste for that buffer.  If bracketed paste is inhiited for at
least one buffer in a terminal, it is disabled for the whole terminal.

* term/xterm.el (xterm-inhibit-bracketed-paste-mode): New mode to
inhibit XTerm bracketed paste per buffer.
(xterm--buffer-terminals, xterm--update-bracketed-paste)
(xterm--bracketed-paste-possible, xterm--is-xterm): New helper
functions.
(xterm--init-bracketed-paste-mode): Remove unused helper
function.
(terminal-init-xterm): Update bracketed paste status when
initializing an XTerm and on window configuration change.

* term.el (term-char-mode, term-line-mode): Inhibit XTerm
bracketed paste in char mode.