Feature: hscroll_indicator (#753)

This is the symetrical of `vscroll_indicator`.

Requested by @ibrahimnasson.

Fixed:https://github.com/ArthurSonzogni/FTXUI/issues/752

src/ftxui/dom/size.cpp

@@ -79,7 +79,7 @@ class Size : public Node {
   Constraint constraint_;
   int value_;
 };
-} // namespace
+}  // namespace
 
 /// @brief Apply a constraint on the size of an element.
 /// @param direction Whether the WIDTH of the HEIGHT of the element must be