Add hints to some text fields for RTL

Having a hint makes sure the cursor is positioned in the right
end of the text field by default for both LTR and RTL locales.
This fixes the user dictionary "add to dictionary" interface
parts, and the "connect to hidden network" interface.

Bug: 8654823
Change-Id: I7c83d35734e53da94bb949e362c5260934ef0b76