Script Modules: Add mechanism to pass data from server to client

[jonsurrell]

One useful feature available to Scripts that Script Modules do not support is a way for the server to send data to the client with the page. Scripts typically do this with wp_add_inline_script.

​Proposal: Server to client data sharing for Script Modules proposes a mechanism for Script Modules to fill this need.

Part of #60647.

Add the print_script_module_data function to the WP_Script_Modules class.

Register hooks to call this function on wp_footer and admin_print_footer_scripts.

​See the Make/Core Proposal and the ​PR in Gutenberg. In summary (from the proposal):

• A new filter runs for each Script Module that is enqueued or in the dependency graph. This filter allows arbitrary data to be associated with a given Script Module and added to the rendered page.
• Script Module data is embedded in the page as JSON in a <script type="application/json"> tag.
• Script Modules are responsible for reading the data and performing their own initialization.

The new filter is "script_module_data_{$module_id}". It should accept and return an array that will be serialized in page HTML (if it is not empty):

add_filter(
        'script_module_data_myModuleID',
        function ( array $data ): array {
                $data['some-data-here'] = 'the client can read this on page load';
                return $data;
        }
);

#6683 includes an example of usage in for Core Script Modules.

Closes #6433 (superseded).

Trac ticket: https://core.trac.wordpress.org/ticket/61510

Committed to Core in https://core.trac.wordpress.org/changeset/58579.

[Bernhard Reiter]

Fixed by [58579].