[ZScript] Skybox Picker Fill

[superhotRussianBird]

SkyPickerFiller - a mapper QoL alternative to SkyPicker for areas with a large amount of sectors. Configured for Ultimate Doom Builder but needs a custom DoomEdNum (https://zdoom.org/wiki/Editor_number).
Instead of spamming SkyPickers manually, place a single SkyPickerFiller to pick a skybox for all connected sectors depending on "Fill type" (Arg2) argument.

How it works:
-"Skybox Viewpoint Tag" (Arg0) and "Apply to" (Arg1) are identical to SkyPicker arguments.
-Fill type 0 "All connected sectors" recursively checks for all sectors connected by shared linedefs.
-Fill type 1 "Separate sector area" works like above, but halts at sectors which don't have F_SKY1 flat on ceiling and/or floor (depending on "Apply to" (Arg1) value).
-Fill type 2 "Sectors by tag" applies to all sectors matching the thing's sector's tag.

-It adds the skybox by messily placing SkyPickers within found sectors - first by locating their center spots, then if that fails locating linedefs instead.
-Also spawns SkyPickers on 3D floor control sectors, although maybe not necessary to do so.