LibGfx+Everywhere: Change Gfx::Rect to be endpoint exclusive

Previously, calling `.right()` on a `Gfx::Rect` would return the last
column's coordinate still inside the rectangle, or `left + width - 1`.
This is called 'endpoint inclusive' and does not make a lot of sense for
`Gfx::Rect<float>` where a rectangle of width 5 at position (0, 0) would
return 4 as its right side. This same problem exists for `.bottom()`.

This changes `Gfx::Rect` to be endpoint exclusive, which gives us the
nice property that `width = right - left` and `height = bottom - top`.
It enables us to treat `Gfx::Rect<int>` and `Gfx::Rect<float>` exactly
the same.

All users of `Gfx::Rect` have been updated accordingly.

Userland/Services/WindowServer/ScreenLayout.ipp

@@ -358,7 +358,7 @@ bool ScreenLayout::try_auto_add_display_connector(DeprecatedString const& device
     for (auto& screen : screens) {
         auto screen_rect = screen.virtual_rect();
         Gfx::IntRect new_screen_rect {
-            screen_rect.right() + 1,
+            screen_rect.right(),
             screen_rect.top(),
             (int)mode_setting.horizontal_active,
             (int)mode_setting.vertical_active