Add the filter to User::is_private() so users can choose to bypass o…

[zacscott]

…r modify this functionality (relates to issue #961)

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What does this implement/fix? Explain your changes.

This change adds a filter graphql_user_model_is_private to the User::is_private() method.

Importantly this filter is BEFORE the normal code of the method is executed and can be used to bypass the rest of the function.

Ordinarily this method does a very expensive query via the use of the count_user_posts() function. This is called multiple times for some GraphQL queries adding considerable load as documented in the issue - #961

This filter can be used to bypass this count_user_posts() at the developers discretion, like so:

add_filter( 'graphql_user_model_is_private', __NAMESPACE__ .'\\graphql_user_model_is_private' );

function graphql_user_model_is_private( $is_private ) {
	return false;
}

Does this close any currently open issues?

This addresses this issue - #961

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

N/A / everything is noted on the issue - #961

Any other comments?

This was based on this declined PR #962

Where has this been tested?

Operating System: Ubuntu 20.04

WordPress Version: 5.6

[coveralls]

Coverage decreased (-0.004%) to 79.662% when pulling 96c50e4 on zacscott:feature/#961-user-model-is-private-filter into 91e1249 on wp-graphql:develop.

[CodeProKid]

I think we should probably handle this in the Model abstract so all models get this. That's how I handled it here: #972.

[jasonbahl]

I've made updates to @CodeProKid original #972 PR to get it to pass tests, and this now allows the filter to run on all Models.

If 3rd party code uses that filter, it will be used. If not, it will fall back to the individual Model's is_private() method.

I'll get that merged and released.

Closing this PR in favor of that one.