Unbranded CodeGen should generate paging operation with Azure Style

[lirenhe]

TypeSpec already includes the support of Paging operation for unbranded: https://typespec.io/docs/standard-library/pagination/

Based on the current agreement, with @list, @pageItems and @nextLink, we could generate the paging operation similar with Azure style.
Please also ensure related models for paging are added into unbranded core.

[weidongxu-microsoft]

A few options

1. generate return model for each API as e.g. ListTodoItemPagedIterable which support stream and iterate (by item and by page).
   apparent downside is that it makes up a name, which also makes it susceptible to naming conflict.
2. generate template e.g. PagedIterable<> which support stream and iterate (by item and by page), then API returns e.g. PagedIterable<TodoItem>
   it could be confusing if multiple such SDK is used together. but fine if only 1 SDK used.
3. Have PagedIterable in clientcore

To me, seems (2) is fine.

[weidongxu-microsoft]

initial design by Srikanta https://gist.github.com/srnagar/e9373153593920dcf1977c928c59e988

[weidongxu-microsoft]

Schedule for pagination for e2e demo on Jan. :

0. Ignore parameters on client-driven pagination for e2e demo, as they are not used in todoApp nor petStore.
1. Decision about whether PagedIterable/PagedResponse models be in clientcore or generated <-- decision: models be in clientcore
2. implement models in clientcore (about 3 weeks, majority of the clientcore effect be parallel from codegen effort)
3. Implement the codegen part (about 2 weeks)

If it goes with the plan, we should be able to get (simple case of) pagination for unbranded in Jan.

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Task breakdown

• [FEATURE REQ] Add PagedIterable and PagedResponse to clientcore azure-sdk-for-java#43358
• [http-client-java] unbranded, generate code for server-side pagination (nextLink) microsoft/typespec#5350