Swift enums/records/errors aren't Equatable or Hashable if they contain object references

[mhammond]

eg

uniffi-rs/uniffi_bindgen/src/bindings/swift/templates/EnumTemplate.swift

Lines 86 to 87 in b46ab54

	{% if !contains_object_references %}
	extension {{ type_name }}: Equatable, Hashable {}

But now that we support objects implementing Eq and Hash we could get a bit smarter and look inside any objects when deciding whether to implement them.