[DMN Designer] Boxed expression view: Expression type label should include spaces

The "Boxed Expression" view (i.e. grid view) shows the name of the type of expression.

At the moment it shows the simple name of the Expression class. It should look up the text to display so that spaces can be included. For example Literal Expression instead of LiteralExpression. The Decision Navigator labels in the left-hand dock are equally affected.