Debuginfo type names for `dyn` types are incomplete

[michaelwoerister]

The current implementation does not handle associated type bindings and auto-traits which leads to information about the type being lost. For example, &dyn Iterator<Item=u32> + Send will be mapped to &dyn Iterator and &dyn Send + Sync will be mapped to & dyn '_.

Some consumers of debuginfo (e.g. NatVis) rely on these type names to be unambiguous identifiers of the type they represent so we must not lose information about assoc type bindings and auto-traits.