Adds support for retrieval of data type references when data type is routed using a GUID

[AndyButland]

Prerequisites

• I have added steps to test this contribution in the description below

Resolves #19182

Description

Although integer IDs are used for backoffice routes in Umbraco 13, we mostly support replacing the integer ID with it's GUID equivalent. But not for data type references as shown in the linked issue.

This PR adds that support so that these requests are resolved.

Testing

• Navigate to a data type that's used on a document type and verify you see the references shown on the "Info" panel.
• Look-up the data type's GUID and manually change the route so this is used in place of the integer ID.
• Verify the references are still shown.

[Copilot]

Pull Request Overview

This PR adds the ability to resolve data type references when a GUID is used in place of the integer ID, supporting a more flexible routing mechanism for data types.

• Introduces a new route attribute for handling GUID requests.
• Adds an overload for GetReferences that accepts a Guid and converts it to an integer id for lookup.

[nikolajlauridsen]

Looks good, and tests good, however it didn't seem right to me to fetch the entire entity to get the ID, so I checked if we could use the IdKeyMap instead, which we can 😄 since I already had already implemented this I decided to just push it, please have a look and see if you agree.

I was gonna do it in 1 commit so it could easily be rolled back, but I forgot to amend, sorry 😅

[AndyButland]

Agreed, that's much better - thanks.