refactor: split AbstractConnectionResolver::get_nodes() and get_edges() into prepare_*() methods

[justlevine]

What does this implement/fix? Explain your changes.

This PR refactors the AbstractConnectionResolver in the following ways:

• ::get_nodes() and ::get_edges() now instantiate AbstractConnectionResolver::$nodes and AbstractConnectionResolver::$edges only once.
• The node generation logic has been relocated from ::get_nodes() into the new ::prepare_nodes() method.
• The edge generation logic has been relocated from ::get_edges() into the new ::prepare_edges() method. The ::prepare_edges() method itself calls the new ::prepare_edge() method, and wraps it in the preexisting graphql_connection_edge filter.

Together, these changes improve the DX by reducing the amount of boilerplate needed when extending the AbstractConnectionResolver class, and improving lifecycle consistency, with potential performance benefits for child classes with complex node/edge generation logic.

There are no breaking changes in this PR.

Important

This PR requires #3120 which should be merged first.

The relevant diff for this PR can be seen at b266d3e

Does this close any currently open issues?

Part of #2749

Any relevant logs, error output, GraphiQL screenshots, etc?

Any other comments?

• The AbstractConnectionResolver::$nodes and ::$edges properties still manually instantiated and graphql_connection_nodes and graphql_connection_edges filters appiled in AbstractConnectionResolver::get_connection(), to maintain b/c compatibility with classes that are currently overloading ::get_edges() and ::get_nodes() directly.

Where has this been tested?

Operating System: Ubuntu 20.04 (wsl2 + devilbox + php 8.1.15)

WordPress Version: 6.5.2

[codeclimate]

Code Climate has analyzed commit b266d3e and detected 0 issues on this pull request.

View more on Code Climate.

[coveralls]

coverage: 84.346% (+0.02%) from 84.33%
when pulling b266d3e on justlevine:dev/prepare-edges-nodes
into cb18964 on wp-graphql:develop.

The merge-base changed after approval.