Add navigation links to type references

These would be helpful in many places. For example, `azcore/arm.ClientOptions` embeds `azcore/policy.ClientOptions`; linking the former to the latter would make reviews easier. To do this we would need to assign unique identifiers to all types discovered while parsing a module (perhaps a qualified name like "github.com/Azure/azure-sdk-for-go/sdk/azcore/policy.ClientOptions") and add those same identifiers to type references (field, parameter, constant, variable types, etc.). That could require significant architectural adjustments in `apiviewgo`. Would also have to take care not to break commenting (you can't comment on navigation links).

Start by reading apiviewgo's module-parsing and type-reference handling, using the azcore/arm.ClientOptions example as the entry point. Define how unique qualified identifiers would connect discovered types and references, then verify that navigation links work without preventing comments on the linked references.

Written by the indexing model from the issue text.