…mall_skin_area

Actually the other way around, so we don't have another negation you have to turn on to turn off (and so the default can be false I suppose). The idea is that recently, a feature was introduced where there should be walls instead of normal skin in small hard to reach places of the model. However, this is to be excluded in most cases for all the top-layer parts exposed to air on the buildplate.

implements CURA-10829

done as part of CURA-10829

…-10829_dont_expose_small_skin_to_air

…nt_expose_small_skin_to_air

Small skin areas replace the normal fill pattern and use walls. Previously in this branch, the possibility was added to not do that to areas exposed to air. It turns out this means in general, not just on the buildplate (also, bottoms can happen away from the buildplate as well of course). As such, take skin bottoms into account of when to exclude areas for consideration when 'Small Top/Bottom On Surface' is off.

part of CURA-10829

Was still left over from the code review for CURA-10670, committed as part of CURA-10829.

…pill.

And the union _with_ prevent_small_exposed_to_air doesn't hurt if the area us 0 anyway.

Done as part of CURA-10829, but fixes a bug found when QA'ing CURA-10670, which was split off and numbered CURA-10945.