Sets the actor's size request in pixels.
This overrides any "normal" size request the actor would have. For example a text actor might normally request the size of the text; this function would force a specific size instead.
height are -1 the actor will use its "normal" size request instead of overriding it, i.e. you can
"unset" the size with -1.
This function sets or unsets both the minimum and natural size.
New width of actor in pixels, or -1
New height of actor in pixels, or -1