Structure View should support expressions as type arguments

[asedunov]

Crystal generics can accept a limited ranged of expressions aside of types, namely:

• numeric literals
• sizeof, instance_sizeof
• offsetof

These arguments must be properly rendered in Structure View. For example:

a : Foo(1, 2.5)

b : Foo(sizeof(X), instance_sizeof(X))

c : Foo(offsetof(X, @z))