output-record-refined-position-test: add gs-clip-mixin specialization
output-record-refined-position-test: add gs-clip-mixin specialization

We don't want the rejected area when clipped to be selectable when
presentation is active. For that we provide a specialization for
gs-clip-mixin to output-record-refined-position-test which calls
region-contains-position-p on the clipping area. Fixes #339.

slyrus/mcclim,slyrus/mcclim