Add useful input method hints to password field by default

Summary: Hint that input methods should treat the password as sensitive and avoid applying "auto-correct" features as well.

Reviewers: Kirigami, ngraham

Reviewed By: Kirigami, ngraham

Subscribers: ngraham, plasma-devel

Tags: Kirigami

Differential Revision: https://phabricator.kde.org/D28316