`building::isImpassableAtCreation` may be misnamed

[ab9rf]

this method (buildingst vmethod slot 0x200) returns true for several building classes that are passable at creation, notably hatches, rollers, slabs, floor grates, and bridges.

analysis of the v50.07 decompilation shows that the implementations of this method always return true for building_animaltrapst, building_axle_horizontalst, building_axle_verticalst, building_bars_floorst, building_bars_verticalst, building_bridgest, building_floodgatest, building_gear_assemblyst, building_grate_floorst, building_grate_wallst, building_hatchst, building_rollersst, building_slabst, building_statuest, building_water_wheelst, building_wellst, building_windmillst, building_window_gemst, and building_window_glassst. all other implementations return always false except for the implementation for building_constructionst which returns true for fortifications and walls, and false for everything else.

in discussion, it has been suggested that this method may instead indicate whether the constructing unit stands on or next to the central square of the building during construction, or whether the building is impassable at construction "if powered"

further research appears needed to properly characterize the purpose of this vmethod; once we better understand its purpose it would probably be appropriate to rename it

[quietust]

Toady's name for this vmethod is perimdestroyer, which seems consistent with the interpretation of "stands next to the building during [de]construction instead of on top of it".

[ab9rf]

sufficiently addressed in #824