Fix variations reference issue - Trac 60309

[kt-12]

What?

Fixes
WordPress/wordpress-develop#5718 (comment)

Detailed issue in the description - https://core.trac.wordpress.org/ticket/60309#ticket

Why?

How?

Testing Instructions

Testing Instructions for Keyboard

Screenshots or screencast

[mukeshpanchal27]

This will not fixed the issue as

gutenberg/packages/block-library/src/navigation-link/index.php

Lines 360 to 363 in 2bc59bd

	if ( $variation['name'] === $name ) {
	unset( $navigation_block_type->variations[ $i ] );
	break;
	}

they check for variation name and remove it.

[Mamaduka]

I think we can also revert changes introduced in #56100. The hook registration order is not important now that variations are lazily evaluated.

[spacedmonkey]

@kt-12 Idea.

We add new function for adding / removing variants. wp_add_block_variation( $variation ) and wp_remove_block_variation( $name ). In core these functions can be implemented using the get_block_type_variations to add and remove elements from that array. In gutenberg these functions can be implement by detecting if the get_variations() method exists on block-type class. If it does, use the filter / overwise, use the variations property directly.

[joemcgill]

The PHPUnit failures have been fixed via #58090 (which is the same approach being suggested here).

If we're going to address directly modifying registered variations as a valid back-compat concern, those PHPUnit tests should be added to the core tests suite that covers the main API for the block type registry, rather than only having tests in this repo for that behavior.