Add missing metadata into placeholder types generated by UnknownTypeResolver

[glopesdev]

With the changes in #1392 the infrastructure was created to inspect package type metadata without actually loading the assembly. This could be leveraged to improve the experience of opening workflows containing types from existing assemblies, but fail to load due to missing dependencies. This would allow us to inject additional missing metadata into the placeholder types, e.g. combinator category and icons or any other content resources, e.g. include workflows.

An important use case for this behavior is automated generation of documentation examples in packages with hardware interface drivers, e.g. Spinnaker where the package depends on the native SDK being installed. In practice it is often not possible to install these kind of SDKs in CI containers such as GitHub actions, so we cannot currently automate exporting of these workflows.