[BT-5120-pagination-ergonomics] Implement queryPage and asyncQueryPage APIs..

[findgriffin]

Description

I added two new methods to FaunaClient along with some refactoring of the error handling. Note that I did not add the full complement of methods with/without QueryOptions and elementClass because I think there are already a lot of methods on FaunaClient.

Note that changing the signature of Page.getAfter from Optional<String> to Optional<AfterToken> is technically a breaking change, but I think this is OK since we are still in beta.

Motivation and context

The feature request was driven by trying to implement a RESTful API in the sample app.

How was the change tested?

There was already a nice E2E test to modify, several unit tests check that we didn't accidentally change the exception handling.

Screenshots (if appropriate):

Change types

• • Bug fix (non-breaking change that fixes an issue)
• • New feature (non-breaking change that adds functionality)
• • Breaking change (backwards-incompatible fix or feature)

Checklist:

• • My code follows the code style of this project.
• • [?] My change requires a change to Fauna documentation.
• • [?] My change requires a change to the README, and I have updated it accordingly.

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