What does this implement/fix? Explain your changes.

This PR improves query handling in AbstractConnectionResolver by making the following changes:

• Implement the new AbstractConnectionResolver::$query_class, ::query_class()and::get_query_class()` methods.
  • ::$query_class() is instantiated once by calling ::get_query_class().
  • ::get_query_class() looks for the $context->queryClass, falling back to the default ::query_class() used by child Connection Resolvers (e.g. PostObjectConnectionResolver). It is then filtered via the new graphql_connection_query_class` filter before being stored on the class property.
  • If ::query_class() is set to null in the child class, the child class will need to overload the ::query() method (see below) or get an error. Similarly an error will be thrown if $context->queryClass is set, but the Resolver doesn't use ::query_class().
• Implement the new ::is_valid_query_class() method which is used by the new ::validate_query_class() method to ensure that overloaded/filtered ::$query_classes are still compatible with the ::query().
• ::get_query() is now implemented in the class, and serves to instantiate AbstractConnectionResolver::$query only once.
• ::get_query() calls the new AbstractConnectionResolver::query() method, which if not overloaded by a child class, instantiates a new ::$query_class().
• A new graphql_connection_pre_get_query filter has been added to allow extenders to short-circuit the ::query() logic without extending the class.

Less importantly,

• AbstractConnectionResolver now uses a PHPStan Generic Type to correctly type-hint queries/query-classes and their associated methods. Extenders who wish to opt into this feature, can use a single @extends doc-block comment on the Connection Resolver class, instead of needing to overload the typehints for all the relevant properties and methods.
• Usage of generic Exceptions have been replaced with an InvariantException when relevant.

There are no breaking changes in this PR.

Todo

• Add tests using $context->queryClass
• Manually test against WPGraphQL for Woocommerce for possible regressions.

Does this close any currently open issues?

fixes #2715
closes #2678

Part of #2749

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

Correct type hints using a non-overloaded AbstractConnectionResolver::$query or ::get_query_method()

Any other comments?

Backwards compatibility is ensured by reinstantiating ::$query and manually applying the graphql_connection_query filter in AbstractConnectionResolver::execute_and_get_ids(). Similarly, direct calls to ::$query in child classes have been left intact. Developers will need to opt into benefit from the new lifecycle and DX improvements, but existing ::get_query() overloads will continue to work as before - quirks and all.

Where has this been tested?

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

WordPress Version: 6.5.2