Added corruption pattern

#11 starting building ui

scripts/expansion_patterns/expansion_square_pattern.gd

@@ -0,0 +1,19 @@
+class_name ExpansionSquarePattern extends ExpansionBase
+
+const EXPANSION_STAGES: int = 3
+
+var expansion_stage: int = 0
+var expansion_tiles: Array[Vector2i] = []
+
+func expand_next_tile() -> Vector2i:
+	if expansion_tiles.is_empty():
+		if expansion_stage < EXPANSION_STAGES:
+			expansion_stage += 1
+			for x in range(-expansion_stage, expansion_stage + 1):
+				for y in range(-expansion_stage, expansion_stage + 1):
+					if abs(x) == expansion_stage or abs(y) == expansion_stage:
+						expansion_tiles.append(Vector2i(x, y))
+	if expansion_stage == EXPANSION_STAGES and expansion_tiles.size() == 1:
+		expansion_finished.emit()
+	
+	return expansion_tiles.pop_at(randi_range(0, expansion_tiles.size() - 1))