Feature: Support for sub-typing handling

[akphi]

Right now we do keep track of subtypes and supertypes in the graph, but for a lot of our checks, we don't handle covariance and contravariance properly.

• [ ] Covariant for union operation class mapping type scanning (e.g. Worker extends Person, so if the target class for the op class mapping is Person, any class mapping for Worker should be listed as well)
• [ ] Expected type label in the lambda editor now does not check for subtype, only strict type equivalent.

[irisyngao]

As we discussed, we should also support:

• [ ] Add support for mapping subtypes in mapping editor UI
• [ ] Enhance the mapping algorithm to take care of subtypes. e.g. Mark parent class as mapped if either subtype is mapped in the query build's explorer tree

[akphi]

We should do this post https://github.com/finos/legend-studio/issues/1070