Password visibility

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• iTerm2 version: Build 3.0.15
• OS version: macOS Sierra 10.12.4
• Attach com.googlecode.iterm2.plist

Detailed steps to reproduce the problem:

1. Change input source (keyboard) to VN-VNI
2. Execute any command under sudo: sudo ls
3. Enter the sudo password

What happened: Password visibility, not hidden in (*) form.

What should have happened: Should be hidden as EN-US input source.

changed milestone to %Review for next version

This would require detecting when we're at a password prompt.

... which you can probably do by looking at the stty settings (canonical mode without local echo).

VTE counterparts:

• this one: https://bugzilla.gnome.org/show_bug.cgi?id=726176
• another related: https://bugzilla.gnome.org/show_bug.cgi?id=755371

Related to issue #3606