Add WP_DISABLE_COLLABORATION constant

[alecgeatches]

Add WP_DISABLE_COLLABORATION constant and wrapper wp_is_collaboration_enabled() function. Based on UI changes in #11310.

WP_DISABLE_COLLABORATION only has a function when it is set to true. Otherwise, the feature can be disabled or enabled via the existing Settings -> Writing checkbox.

Trac ticket: https://core.trac.wordpress.org/ticket/64904

Screenshots

With

define('WP_DISABLE_COLLABORATION', true );

---

With

define('WP_DISABLE_COLLABORATION', false );

or no WP_DISABLE_COLLABORATION configuration at all, the default checkbox:

Use of AI Tools

AI assistance: Yes
Tool(s): Claude
Model(s): Opus 4.6
Used for: Implementation

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[peterwilsoncc]

I have a few of suggestions.

1. Instead of a constant with a negative intent, it is clearer to use a positive intent. This avoids having code along the lines of if ( CONSTANT === true ) then false;
2. It's more precise to describe the constant as whether or not RTC is permitted, than whether RTC is enabled or disabled. I think WP_ALLOW_COLLABORATION is a better match for that intent.
3. As a part of the consideration is to allow hosts to disallow the feature at an environment level, allowing an environment variable to be set will help meet their needs
4. Instead of needing to repeat the ! defined() && ..., define the default value in wp_functionality_constants()

My suggestion is to add the following to wp_functionality_constants() and modify the PR for the various implications

/**
 * Whether real time collaboration is permitted to be enabled.
 *
 * @since 7.0.0
 */
if ( ! defined( 'WP_ALLOW_COLLABORATION' ) ) {
	if ( false !== getenv( 'WP_ALLOW_COLLABORATION' ) ) {
		// Environment variable is defined.
		if ( 'true' === getenv( 'WP_ALLOW_COLLABORATION' ) ) {
			define( 'WP_ALLOW_COLLABORATION', true );
		} else {
			define( 'WP_ALLOW_COLLABORATION', false );
		}
	} else {
		// Environment variable is not defined, default to true.
		define( 'WP_ALLOW_COLLABORATION', true );
	}
}