The relation between the pressure/size and the pressure/alpha is a
fundamental property that defines the behavior of a brush, so it does
not make sense to have it unified across all brushes. This applies both
for sculpting and painting.
Some of the new 2.82 brushes need pressure/size or pressure/alpha to be
enabled to work propely, while others don't. Users should not be
switching on and off this property manually when changing brushes if they
want to use unified size. This is also causing that some users are using
the brushes with an incorrect configuration.
Reviewed By: jbakker
Differential Revision: https://developer.blender.org/D6291
9251b07720