Facilitate Optimization Detective to be embedded in other plugins/themes

[westonruter]

Feature Description

To increase the reach of the optimizations made possible by Optimization Detective, the plugin should be able to be embedded in popular plugins and themes without having to explicitly install the Optimization Plugin. In talking with Elementor at the WordCamp Asia Contributor Day, they pointed me to the plugin bootstrap file in woocommerce/action-scheduler as a way to do this.

Let's say someone installs the Optimization Detective plugin while the logic is also embedded in 2 other plugins as well as in a theme: only the copy with the most recent version should end up getting loaded. Additionally, if versions match between two copies, then the version in the actual Optimization Detective plugin should be favored.

This should also be explored for Embed Optimizer.

[westonruter]

Additionally, it may make sense for embedders to skip the output-buffering added in:

performance/plugins/optimization-detective/hooks.php

Line 13 in 26c83e7

add_filter( 'template_include', 'od_buffer_output', PHP_INT_MAX );

performance/plugins/optimization-detective/hooks.php

Line 15 in 26c83e7

add_action( 'wp', 'od_maybe_add_template_output_buffer_filter' );

If the plugin is already doing output buffering, they may want to manually pass the buffer through od_optimize_template_output_buffer() (if od_can_optimize_response() returns true). For example, a plugin may want to do this:

<?php
ob_start( static function ( string $buffer ) {
	// Do plugin-specific processing.
	// ...
	
	// Apply Optimization Detective.
	if (
		function_exists( 'od_can_optimize_response' ) &&
		od_can_optimize_response() &&
		function_exists( 'od_optimize_template_output_buffer' )
	) {
		$buffer = od_optimize_template_output_buffer( $buffer );
	}
	
	return $buffer;
} );

To prevent double-processing, they currently would have to do the following to unhook the plugin's own output buffering:

remove_filter( 'template_include', 'od_buffer_output', PHP_INT_MAX ); 
remove_action( 'wp', 'od_maybe_add_template_output_buffer_filter' );