Hide password form fields by default (#3991)

* Hide password form fields by default

* Trying to bypass enforced autocompletion by just having a test field at first

Something like onfocus didn't work, you'd tab through form elements
and unless you filled in the user name, changing the form field to
password would cause it to autocomplete.

It looks like, at least in Mac/Firefox, going from plain text to password
in the 'oninput' event handler works. The plain text is revealed neither
with typing nor pasting.

* Update core/src/main/resources/lib/form/password.jelly

Co-Authored-By: daniel-beck <daniel-beck@users.noreply.github.com>

* Use previously defined value

* Make new password form fields opt-out

* Add support for redacting form secrets in new password field

* Have a password value pre-set in Jelly

* Fix method

* Fix test by clicking on the button to change the password

* Forgot period separator between class and property name

core/src/main/java/hudson/Functions.java

@@ -386,6 +386,11 @@ public class Functions {
         return null;
     }
 
+    @Restricted(NoExternalUse.class)
+    public static boolean useHidingPasswordFields() {
+        return SystemProperties.getBoolean(Functions.class.getName() + ".hidingPasswordFields", true);
+    }
+
     /**
      * URL decomposed for easier computation of relevant URLs.
      *