[Wi-Fi] Improve contrast of edit text hint

Extend the style from TextAppearance.Widget.EditText which
has hint color of #808080 and contrast ratio 3.95

Bug: 146908018
Test: Manual visual
      Accessibility scanner shows contrast ratio 3.95

Change-Id: Ie20e750095af30a217166cdffeda2e29cec970e3
2 files changed