Reworked Output::ImplGetGradientSteps to be usable for both linear and
complex (actually, axial, but that's another story) gradients by adding
a default parameter.

This gets rid of another meOutDevType from gradient functions

Change-Id: I1dc918e4c3153617d172560523cfca303f0b904c
Reviewed-on: https://gerrit.libreoffice.org/8872Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>