Improving selection at Editing side.
The setSelection algorithm should take Regions into account when traversing the RenderTree.
Set SelectionNone in Regions when clearing the selection.
Set SelectionStart/SelectionEnd to the Region blocks (if necessary)
repaintSeleciton should take Regions into account when traversing the RenderTree.
Improving the block gaps filling.
Set SelectionInside flag to the RenderRegion blocks.
Avoid fill the vertical gap for RenderNamedFlowFragment
Do not fill gaps for regions as they are already filled by the RenderNamedFlowThread
Use bottom of region just before lastLogicalTop
Move the update of lastLogicalTop out of the for loop
Fix bug in the selecitonRepaint function.
Implenenting a new Range::toString method, considering RenderRegion blocks.