Add test cases for patch.force_edgecolor behavior with facecolor="none" - #29690

This codifies current behavior. It does not fix #29690, but is a baseline so that we can do a reliable refactoring to fix #29690 without accidentally changing current behavior (see #29261 (comment)).

@timhoffm In the current behavior, when patch.force_edgecolor=False and facecolor="none", the artist becomes fully transparent (invisible). Should we first address this specific issue in the existing patch.force_edgecolor logic, or should we focus on #29261?

Sorry, I always get a knot in my brain when I try to think though all cases 😵. The fundamental goal of #29261 is to get rid of the confusing patch.force_edgecolor. I'm not clear whether we need to to fix a behavior that depends on that first. Ultimately, we want new parameters

#patch.edgecolor: "none"            # default edgecolor for Patch and Collection
#patch.edgecolor_fallback: "black"  # edgecolor to be used if facecolor is "none" to prevent completely invisible artists

and an as-smooth-as possible transition path to them - i.e. give themes/users with customized patch.force_edgecolor/patch_edgecolor alternatives to configure their behavior through the new parameters.

I suspect, but right now can't tell reliably, that changing part of the logic of patch.force_edgecolor before does not add a benefit because that'll be a breaking change, and we can as well do the break during the migration if needed. Therefore, I suggest that you move forward on #29261 and we'll see how well that goes. At worst, we'll have to take a step back, do the change patch.force_edgecolor and then come back to #29261 afterwards.