refactor: make AbstractConnectionResolver::should_execute() non-abstract and add ::pre_should_execute()

[justlevine]

What does this implement/fix? Explain your changes.

This PR refactors the DX around AbstractConnectionResolver::should_execute().

More specifically:

• AbstractConnectionResolver::$should_execute is no longer instantiated with a value. Instead ::should_execute() is no longer abstract and returns true by default, so only Resolvers that require custom should_execute logic need to overload the method.
• Resolver-specific pre_should_execute logic has been abstracted out of AbstractConnectionResolver's constructor and into a new ::pre_should_execute() method. This overloadable method is then wrapped in a new ::get_pre_should_execute() method which uniformly filters the value with the new graphql_connection_pre_should_execute hook.
• ::get_should_execute() has been modified to call ::should_execute() if the class property has yet to be set. This ensure backwards compatibility and paves the way for future enhancements, such as improving the evaluation logic and filtering in ::execute_and_get_ids().

There are no breaking changes in this PR.

Does this close any currently open issues?

Part of #2749

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

Any other comments?

• Due to the way these changes are implemented, this PR is fully backwards compatible. Existing Resolvers will continue to work as before, and developers will be able to update their classes at their leisure to "opt in" to the new features like moving their constructor pre-checks into get_pre_should_execute(), separating the pre/should_execute logic, and removing unnecessary parameter instantiation, method overloading.

Where has this been tested?

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

WordPress Version: 6.5.2

[coveralls]

coverage: 84.275% (-0.01%) from 84.289%
when pulling 8014e2c on justlevine:dev/cr2-backport/refactor-should_execute
into a66f3e1 on wp-graphql:develop.

[jasonbahl]

Left a comment regarding a @todo comment

[codeclimate]

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