layouts: Adjust layout-sizes to the correct aspect-ratios

and fix some other issues, to make the layouts more consistent.

The aspect-ratios of the layouts,
should now match the intended aspect-ratios (12:7 and 16:5),
with 3 decimal-digits of precision; either exactly,
or rounded to be a little more square,
so that the entire height of the panel will be used.
Adding 0.001 to `width` in the `default`-outlines of the layouts,
would make the layouts a little wider than the intended aspect-ratio.

Part-of: <https://gitlab.gnome.org/World/Phosh/squeekboard/-/merge_requests/691>

data/keyboards/pin/us.yaml

@@ -1,7 +1,8 @@
 ---
 margins: { top: 4, side: 0, bottom: 4 }
 outlines:
-    default: { width: 120, height: 52 }
+    default: { width: 123.428, height: 52 }
+    special: { width: 123.428, height: 52 }
 
 views:
     base:
@@ -12,9 +13,10 @@ views:
 
 buttons:
     BackSpace:
+        outline: "special"
         icon: "edit-clear-symbolic"
         action: "erase"
     Return:
+        outline: "special"
         icon: "key-enter"
         keysym: "Return"
-