[Apollo Pagination] Improve ReversePagination support, implement loadAll support, Bidirectional Pagination

[Iron-Ham]

What are you trying to accomplish?

1. I want consumers of the GraphQLPager to be able to load all pages at once, should they desire to do so.
2. In a quest to deliver bidirectional pagination, we must first solidify support for reverse pagination.

closes apollographql/apollo-ios#3265

What approach did you choose and why?

LoadAll Support:
First, I modified the fetch function to follow async/await syntax. That's so that we can await its return prior to beginning to loop over loadMore.

Then, I implemented the function using a while loop.

Finally, I made additive changes to the MockGraphQLServer to support subsequent loads of this nature.

Reverse Pagination:
Leaning hard into differentiating reverse and forward pagination from one another.
If we are to support both types of pagination at once, then they must be treated as being separate from one another: A page can be a previous page or it can be a next page. It cannot be both.

BIdirectional Pagination
Once reverse pagination was solidifed, this was a breeze to implement. It basically amounted to defining the pagination struct.

Anything you want to highlight for special attention from reviewers?

Note that the output for the pagination controller is now a struct. This allows us to make changes to the output without breaking previous versions. I've removed logic around Task and Continuation management.

If something goes wrong, what are the mitigation strategies?

• Rollback - This change can only be disabled by reverting this pull request or commit.

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Copilot Summary

This pull request primarily introduces improvements to the Apollo GraphQL testing suite and pagination functionality. The most significant changes include the addition of a new BidirectionalPaginationTests class for testing bidirectional pagination, modifications to the MockGraphQLServer class to enhance testing capabilities, and updates to the AnyGraphQLQueryPagerTests and ForwardPaginationTests classes to accommodate new pagination functionalities.

Enhancements to Apollo GraphQL testing:

• Tests/ApolloInternalTestHelpers/MockGraphQLServer.swift: Added a private subscript to the MockGraphQLServer class to handle request expectations for a given operation type. Also, a new expect method was added to handle request expectations for a specific operation. [1] [2]

Improvements to Apollo GraphQL Pagination:

• Tests/ApolloPaginationTests/AnyGraphQLQueryPagerTests.swift: Modified the eraseToAnyPager method to include an additional parameter. Also, added a new test_loadAll method to test the loading of all pages. Several other minor changes were made to accommodate updates to the pagination functionality. [1] [2] [3] [4]
• Tests/ApolloPaginationTests/ForwardPaginationTests.swift: Updated several methods to reflect changes in the pagination functionality. [1] [2] [3] [4] [5]
• Tests/ApolloPaginationTests/ConcurrencyTest.swift: Updated several methods to reflect changes in the pagination functionality. [1] [2] [3] [4] [5] [6]

Addition of new test class:

• Tests/ApolloPaginationTests/BidirectionalPaginationTests.swift: Added a new BidirectionalPaginationTests class to test bidirectional pagination functionality. This class includes several methods to test fetching multiple pages, loading all pages, and more.

[AnthonyMDev]

Couple of minor things, but this is looking good!

[AnthonyMDev]

Couple of minor things, but this is looking good!