LibWeb: Store the input image button's selected coordinates as integers

The spec has prose which states, e.g., "The x-component must be a valid
integer".

Userland/Libraries/LibWeb/HTML/HTMLInputElement.h

@@ -105,8 +105,8 @@ public:
     WebIDL::ExceptionOr<void> set_size(unsigned value);
 
     struct SelectedCoordinate {
-        double x { 0.0 };
-        double y { 0.0 };
+        int x { 0 };
+        int y { 0 };
     };
     SelectedCoordinate selected_coordinate() const { return m_selected_coordinate; }