Swift - adds support for setting the raw url of a request builder

[baywet]

related microsoft/kiota#628
to avoid people having to drop the whole generated experience when they already have a URL (delta) or need to build one themselves (expansion limitations for drives), request builders should have a constructor that accepts a request adapter and a raw url (string)
This constructor can either be an overload or a union type for the path parameters if that makes sense.
If a string is provided, set it to
aw-request-url in the path paramters. (generation)
In the abstractions update the URI getter to parse and return that url if provided on this key see the dotnet implementation