Add a _doing_it_wrong() to WP_Block_Patterns_Registry::register() when hooked but not on init.

[costdev]

Trac ticket: https://core.trac.wordpress.org/ticket/55655

[hellofromtonya]

See my comments here WordPress/gutenberg#40736 (comment) about forcing registration to only be when hooked to init. I'm wondering what the impact to extenders will be.

[peterwilsoncc]

See my comments here WordPress/gutenberg#40736 (comment) about forcing registration to only be when hooked to init. I'm wondering what the impact to extenders will be.

I think it will be problematic.

Both post types and taxonomy require developers wait until the init hook or later to register a custom object. As the init hook is relatively early, later registration can come in handy when the developer wishes to know something about the request when registering the custom object.

That may also be the case here where waiting for the query to be parsed may be helpful.

[hellofromtonya]

Notice at the end of WP_Block_Patterns_Registry::register() there's code to detect and store a pattern not registered on init. The code in this PR would bail out before that code and the subsequent code that works with the registered_patterns_outside_init property. In other words, a _doing_it_wrong() with an early bail-out negates the tracking and use case of the registered_patterns_outside_init property and its usage.