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/ClassicWindowTheme.cpp

@@ -36,7 +36,7 @@ Gfx::IntRect ClassicWindowTheme::titlebar_icon_rect(WindowType window_type, cons
         16,
     };
     icon_rect.center_vertically_within(titlebar_rect);
-    icon_rect.move_by(0, 1);
+    icon_rect.translate_by(0, 1);
     return icon_rect;
 }