fix(rust): oneOf generation for client (#17915)

* fix(rust): discriminator mapping to serde rename

Discriminator mapping has been ignored in some cases.
Even existing samples had wrong definition in some cases

This PR addresses this

* fix(rust): `oneOf` generation for client

Solves #17869 and #17896 and also includes unmerged $17898

Unfortunately it affects quite a lot of code, but we can see that only client-side models were affected by re-generation.
I tried to split this PR to several, but they're really coupled and hard to create a chain of PRs.

* fix: indentation in `impl Default`

* missing fixes

* fix: correct typeDeclaration with unaliased schema

* style: improve indentation for models

* fix: user toModelName for aliases of oneOf

* refactor: unify `getTypeDeclaration` for rust

* cover the case when `mapping` has the same `ref` for different mapping names

* test: add test for previous change

* style: remove extra qualified path to models

* add some comments

* fix(build): use method of `List` instead of specific for `LinkedList`

samples/client/others/rust/reqwest/emptyObject/docs/DefaultApi.md

@@ -10,7 +10,7 @@ Method | HTTP request | Description
 
 ## endpoint_get
 
-> crate::models::EmptyObject endpoint_get()
+> models::EmptyObject endpoint_get()
 Get endpoint
 
 ### Parameters
@@ -19,7 +19,7 @@ This endpoint does not need any parameter.
 
 ### Return type
 
-[**crate::models::EmptyObject**](EmptyObject.md)
+[**models::EmptyObject**](EmptyObject.md)
 
 ### Authorization