Warn on unknown layout properties

With the Lua ui API it is very easy to make mistakes by putting properties in the wrong place, or mistyping them. This is frustrating to debug as there is no feedback/warning on unknown properties so it's very easy to miss what's wrong. Especially small upper/lower case mistakes such as autosize vs autoSize.

For example. I spent a lot of time debugging why this Image layout wasn't working:

        icon = {
            type = ui.TYPE.Image,
            resource = ui.texture{path = tex},
            props = {
                size = V2(56, 56),
                position = V2(30, 27),
                anchor = V2(0.5, 0.5),
            },
        }

A warning in the log along the lines of 'resource' is not a valid member of a widget of type Image would have made debugging this much faster.

similar for the props table. I spent a lot of time wondering why alignment and word wrap wasn't working for Text simply because i had mistyped autoSize as autosize. A warning in the log notifying me that 'autosize' is not a valid property of a widget of type Text would have made debugging this much faster.