UI Library component properties with custom types

**Is your feature request related to a problem? Please describe.**
You can have custom types (== types without @model directive) in graphql api, but cant use them in UI Library component properties.
Component properties can be only of model or scalar types.

**Describe the solution you'd like**
It would be very useful to have component properties with custom types, too.

**Additional context**

Start in the UI Library component-property flow and reproduce the issue with a GraphQL API custom type that lacks the @model directive. Trace where property types are limited to models or scalars; done means custom GraphQL types can be selected and used as component properties.

Written by the indexing model from the issue text.