LibGfx: Unify Rect, Point, and Size

This commit unifies methods and method/param names between the above
classes, as well as adds [[nodiscard]] and ALWAYS_INLINE where
appropriate. It also renamed the various move_by methods to
translate_by, as that more closely matches the transformation
terminology.

Userland/Libraries/LibGfx/Path.cpp

@@ -50,7 +50,7 @@ void Path::elliptical_arc_to(const FloatPoint& point, const FloatPoint& radii, d
         }
 
         // Move the endpoint by a small amount to avoid division by zero.
-        next_point.move_by(0.01f, 0.01f);
+        next_point.translate_by(0.01f, 0.01f);
     }
 
     // Find (cx, cy), theta_1, theta_delta