Allow renderType: Text.NativeRendering on retina displays/devices

Setting the renderType to Text.NativeRendering might be needed in some
cases where distance-field does not produce the expected results, such
as for emoji characters or really large fonts. These use cases are
valid on retina displays as well, so having the setter second-guess
the request from the user to use native rendering is not ideal.

Change-Id: I7c6049766e60574487c29de07fbd5c100ec69a2a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>