tiling: Make child tiles inherit padding from parent tile

If a new tile is added, make it inherit parent tile's padding to ensure
consistent padding.

BUG: 465842

src/tiles/tile.cpp

@@ -26,6 +26,9 @@ Tile::Tile(TileManager *tiling, Tile *parent)
     , m_parentTile(parent)
     , m_tiling(tiling)
 {
+    if (m_parentTile) {
+        m_padding = m_parentTile->padding();
+    }
     connect(Workspace::self(), &Workspace::configChanged, this, &Tile::windowGeometryChanged);
 }