fix!: Keep `PageField` with previous page data when filtering `formFields` by `pageNumber`.

[justlevine]

What

This PR changes the behavior of the pageNumber filter on Form Fields connection, so that GF_Field_Page is included in the results for the previous pageNumber.

This is a breaking change.

Why

As noted in https://github.com/AxeWP/wp-graphql-gravity-forms/issues/208#issuecomment-2043083723, the Page field includes the data required to create back/next buttons for the page number preceeding it. But because the pageNumber is is for the upcoming page, it misses the field field.

How

Testing Instructions

Additional Info

Checklist:

• [x] This PR is tested to the best of my abilities.
• [x] This PR follows the WordPress Coding Standards.
• [x] This PR has proper inline documentation.
• [x] This PR has unit tests to verify the code works as intended.
• [x] The changes in this PR have been noted in CHANGELOG.md