layout: Incrementalize reflow of block formatting contexts impacted by

floats, and make float placement idempotent.

This moves float placement outside sequential block size computation.

Improves the maze solver.

components/layout/table_wrapper.rs

@@ -301,6 +301,10 @@ impl Flow for TableWrapperFlow {
         self.block_flow.compute_absolute_position()
     }
 
+    fn place_float_if_applicable<'a>(&mut self, layout_context: &'a LayoutContext<'a>) {
+        self.block_flow.place_float_if_applicable(layout_context)
+    }
+
     fn assign_block_size_for_inorder_child_if_necessary<'a>(&mut self,
                                                             layout_context: &'a LayoutContext<'a>)
                                                             -> bool {