Check boundary condition before throwing "structure bounds that extend exactly at boundares" warning

[tomflexcompute]

If a structure has bounds exactly at the simulation domain boundaries, it throws a warning about it despite what boundary condition is applied. For periodic, Bloch, and PEC/PMC, having structures touching should be fine? Maybe we can check the boundaries first to see if it's an absorbing boundary and warn only in this case?

[momchil-flex]

@weiliangjin2021 for periodic/Bloch is it still needed to extend structures to get the right update coefficients? I think you now handle periodicity correctly in preprocessing so it should not be needed but not sure?

[weiliangjin2021]

@weiliangjin2021 for periodic/Bloch is it still needed to extend structures to get the right update coefficients? I think you now handle periodicity correctly in preprocessing so it should not be needed but not sure?

I believe not needed now, at least the point containment building part is fine