Chore: Review FrameContainer constructors for shared dimen objects

Nothing else seems problematic, this is mostly just cosmetic sanitization
around Geom objects.

frontend/ui/widget/container/widgetcontainer.lua

@@ -55,6 +55,7 @@ function WidgetContainer:paintTo(bb, x, y)
         self.dimen = Geom:new{x = 0, y = 0, w = content_size.w, h = content_size.h}
     end
 
+    -- NOTE: Clunky `or` left in on the off-chance we're passed a dimen that isn't a proper Geom object...
     x = x + (self.dimen.x or 0)
     y = y + (self.dimen.y or 0)
     if self.align == "top" then