Interactivity API: Avoid unnecessary processing of directives

[joemcgill]

During performance reviews on 6.5, it was discovered that processing directives of interactive blocks can sometimes be the source of degraded performance.

This is because all block types that support interactivity are getting processed by wp_interactivity_process_directives_of_interactive_blocks even if the block markup didn't contain the necessary data-wp- markup necessary for processing, resulting in unnecessary calls to wp_interactivity_process_directives which make heavy use of the WP_HTML_Tag_Processor.

We should try to avoid this unnecessary processing if possible.

This is a modified PR based on @gziolo's ​initial approach in this Slack thread.

The main change from his original proposal is to use str_contains() instead of str_pos() given that we have a polyfill for this in Core now. This reduces calls to wp_interactivity_process_directives() on the Twenty Twenty-four homepage from 9 to 1 along with memory consumption related to the WP_HTML_Tag_Processor.

Trac ticket: https://core.trac.wordpress.org/ticket/60749

[gziolo]

@swissspidy, it would be nice to have this fix included as well.

[swissspidy]

In 57824:

Interactivity API: Do not process directives when there aren’t any.

Short-circuits directive processing when the markup does not actually contain any data-wp-* attributes.
This reduces function calls and memory usage for the best case scenario due to not involving WP_HTML_Tag_Processor.

Props joemcgill, swissspidy, gziolo, cbravobernal, flixos90.
Fixes #60749.

[swissspidy]

In 57825:

Interactivity API: Do not process directives when there aren't any.

Short-circuits directive processing when the markup does not actually contain any data-wp-* attributes.
This reduces function calls and memory usage for the best case scenario due to not involving WP_HTML_Tag_Processor.

Reviewed by gziolo, swissspidy.
Merges [57824] to the to the 6.5 branch.

Props joemcgill, swissspidy, gziolo, cbravobernal, flixos90.
Fixes #60749.

Merged in https://core.trac.wordpress.org/changeset/57824 and https://core.trac.wordpress.org/changeset/57825

[gziolo]

I'm playing with another idea when I completely avoid using hooks by moving the logic to the WP_Block class:

​https://github.com/WordPress/wordpress-develop/pull/6331