go.crypto/ssh/terminal: support bracketed paste mode.

Some terminals support a mode where pasted text is bracketed by escape sequences. This is very useful for terminal applications that otherwise have no good way to tell pastes and typed text apart.

This change allows applications to enable this mode and, if the terminal supports it, will suppress autocompletes during pastes and indicate to the caller that a line came entirely from pasted text.

LGTM=bradfitz
R=bradfitz
CC=golang-codereviews
https://golang.org/cl/171330043
2 files changed