Apply theme by using notification context

Apply theme by using notification context instead of
SystemUI context when loading notification icon drawable.

When loading notification icon for StatusBarIconView, use
notification's context as parameter, then applyTheme will
find theme resource in notification package and avoid
finding wrong theme resource in SystemUI for other apply's
drawable resources.

Bug: 158126029

Change-Id: Iaf8d8c6ff4af988233a1a331b255f6a4b44ca6cb