Fix widget drop preview outline on 4x5 grids

=> We were not account for mBorderSpacing in the outline calculation
=> This was fine in most cases as this value is 0, but 4x5 appears to be the exception

Bug: 194227752

Test: manual, see video in bug.
Change-Id: Ib590bc142a0f65e75f92ee057f8b4f4b0f81521b

src/com/android/launcher3/CellLayout.java

@@ -566,9 +566,10 @@ public class CellLayout extends ViewGroup {
                 int spanX = mDragOutlines[i].cellHSpan;
                 int spanY = mDragOutlines[i].cellVSpan;
 
+                // TODO b/194414754 clean this up, reconcile with cellToRect
                 mVisualizeGridRect.set(paddingX, paddingY,
-                        mCellWidth * spanX - paddingX,
-                        mCellHeight * spanY - paddingY);
+                        mCellWidth * spanX + mBorderSpacing * (spanX - 1) - paddingX,
+                        mCellHeight * spanY + mBorderSpacing * (spanY - 1) - paddingY);
 
                 int transX = x * mCellWidth + (x * mBorderSpacing)
                         + getPaddingLeft() + paddingX;