Interop Gen: Support Qualified Names

[nikeokoronkwo]

TS makes use of qualified names when referencing types in namespaces, typeof types that reference properties in nested declarations (such as enums, classes, interfaces), when referencing and more.

Dart does not support such syntax for naming, and so such declarations and types need to be mapped to their respective imports, declarations, etc.

This issue is for adding support for qualified names like these in the Dart JS Interop Interface Generator.