Fix swapped spacing bug in BoxGrid

The horizontalSpacing and verticalSpacing was swapped when calculating
the size of the spanned cell in BoxGrid.
This fix corrects the calculation.

Author: cheonjaeung

grid/src/commonMain/kotlin/com/cheonjaeung/compose/grid/BoxGridMeasurePolicy.kt

@@ -144,9 +144,9 @@ private class BoxGridMeasureHelper(
             }
 
             val cellWidthConstraints = cellWidthConstraintList[columnPosition] * columnSpan +
-                verticalSpacingPx * (columnSpan - 1)
+                horizontalSpacingPx * (columnSpan - 1)
             val cellHeightConstraints = cellHeightConstraintList[rowPosition] * rowSpan +
-                horizontalSpacingPx * (rowSpan - 1)
+                verticalSpacingPx * (rowSpan - 1)
 
             val placeableConstraints = Constraints(
                 minWidth = if (fillCellWidth) cellWidthConstraints else 0,

grid/src/test/java/com/cheonjaeung/compose/grid/BoxGridSpanTest.kt

@@ -216,4 +216,43 @@ class BoxGridSpanTest {
             }
         }
     }
+
+    @Test
+    fun testSpanWithSpacing() {
+        paparazzi.snapshot {
+            BoxGrid(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .background(Color.LightGray),
+                rows = SimpleGridCells.Fixed(4),
+                columns = SimpleGridCells.Fixed(4),
+                horizontalSpacing = 32.dp,
+                verticalSpacing = 8.dp,
+            ) {
+                Box(
+                    modifier = Modifier
+                        .position(row = 0, column = 0)
+                        .span { BoxGridItemSpan(row = 2) }
+                        .background(Color.Blue)
+                )
+                Box(
+                    modifier = Modifier
+                        .position(row = 1, column = 1)
+                        .span { BoxGridItemSpan(row = 2) }
+                        .background(Color.Green)
+                )
+                Box(
+                    modifier = Modifier
+                        .position(row = 2, column = 2)
+                        .span { BoxGridItemSpan(row = 2, column = 2) }
+                        .background(Color.Yellow)
+                )
+                Box(
+                    modifier = Modifier
+                        .position(row = 0, column = 1)
+                        .background(Color.Red)
+                )
+            }
+        }
+    }
 }