Add unit tests for block_has_support

[ntsekouras]

Trac ticket: https://core.trac.wordpress.org/ticket/53257

This PR just adds some unit tests for block_has_support function.

What I wanted to verify though is if this is the expected behavior in the case we have declared supports for a key with an empty array. Should this return true as it does now?

Example test that passes with an empty array:

public function test_block_has_support_empty_array() {
	$this->registry->register(
		'core/example',
		array(
			'supports' => array(
				'align' => array(),
			),
		)
	);
	$block_type = $this->registry->get_registered( 'core/example' );
	$align_support = block_has_support( $block_type, array( 'align' ) );
	$this->assertSame( $align_support, true );
}

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[gziolo]

What I wanted to verify though is if this is the expected behavior in the case we have declared supports for a key with an empty array. Should this return true as it does now?

You can file an issue to discuss it separately. It's an edge case that you don't see in a real life. I believe it should return false but it's also could be considered wrong input data like providing a number.

[gziolo]

Committed in https://core.trac.wordpress.org/changeset/50955.