[MC-279834] painting entities in structures are misplaced / shifted

Paintings of sizes other than 3x3 and 1x1 are shifted after saving and loading a structure.

There are some odd inconsistencies with placing paintings from creative inventory. Lower left corner is

Size	Placing	Pos X Y	Structure offset
4x4	-1 -1	1.0 0.0	1 1
4x3	-1 -1	1.0 0.5	1 0
3x4	-1 -1	0.5 0.0	0 1
3x3	-1 -1	0.5 0.5	0 0
4x2	-1 0	1.0 0.0	1 1
2x2	0 0	1.0 0.0	1 1
2x1	0 0	1.0 0.5	1 0
1x2	0 0	0.5 0.0	0 1
1x1	0 0	0.5 0.5	0 0

Placing column; offset to lower left corner from the block which was clicked

Pos X Y; offset in Pos[] from TileXYZ values

Structure; observed shift in placement when saving/loading a structure

Placing is jarring, but doable. Structures however requires editing the structure nbt files to compensate.