NativeUtil: Use UTF-8 decoder

Most of the string/hex fields that is exposed in WifiConfiguration
wrongly state that the field neeeds to be a quoted ASCII string or hex.
It turns out that the fields could be any UTF-8 encoded string.

Bug: 64586263
Test: Unit tests
Change-Id: I3c761d10018ccb944c0623935cfa6b60cedcbfd8
4 files changed