[LLC][Core] Prove grow-up story for Pageables

[annelo-msft]

There are currently tests for the grow-up story for one GET operations in Azure.Core.Experimental's Tests project:

• LLC Test
• Model Cast Test
• Error Response Test

We would like to add tests that prove the grow-up story for Pageables as well. These should:

• Test that LLC returns Pageable<BinaryData> for a Pageable method
• Test that BinaryData can be cast to OutModel
• Test that a grow-up helper method can be added that returns Pageable<OutModel>

[annelo-msft]

Initial work done on Pageables here, before handing off to Alexander.

[annelo-msft]

Duplicate of Azure/autorest.csharp#1944