Sets whether the contents of the entry are visible or not.
When visibility is set to false, characters are displayed as the invisible char, and will also appear that way when the text in the entry widget is copied elsewhere.
By default, GTK+ picks the best invisible character available in the current font, but it can be changed with set_invisible_char.
Note that you probably want to set input_purpose to gtk_input_purpose_password or gtk_input_purpose_pin to inform input methods about the purpose of this entry, in addition to setting visibility to false.
true if the contents of the entry are displayed as plaintext