Build/QA: Retire nullCoalesce.property baseline

[huzaifaalmesbah]

Description

This PR resolves all occurrences of nullCoalesce.property and completely retires tests/phpstan/baselines/nullCoalesce.property.neon:

1. src/wp-includes/class-wp-locale.php:
   $this->word_count_type is uninitialized / null until init() calls get_word_count_type(), which uses $this->word_count_type ?? _x( 'words', ... ) to fall back to the localized word count translation. Updating the property's PHPDoc @var tag from string to string|null accurately documents its lifecycle and resolves the nullCoalesce.property static analysis error without breaking locale-specific word/character counting.

2. src/wp-includes/general-template.php:
   WP_Query::$max_num_pages is non-nullable (int). Adjusted $wp_query->max_num_pages ?? 1 to ! empty( $wp_query->max_num_pages ) ? $wp_query->max_num_pages : 1 to preserve correct fallback when max_num_pages is 0.

3. src/wp-includes/rest-api/endpoints/class-wp-rest-post-types-controller.php:
   WP_Post_Type::$template is initialized as array(). Simplified $post_type->template ?? array() to $post_type->template.

Testing Instructions

1. Run composer phpstan locally to verify 0 errors.
2. Run locale and formatting unit tests:

   npm run test:php -- --filter=Tests_Formatting_wpTrimWords
   npm run test:php -- --filter=paginate_links

3. Run PHPCS to verify coding standards:

   vendor/bin/phpcs src/wp-includes/class-wp-locale.php src/wp-includes/general-template.php src/wp-includes/rest-api/endpoints/class-wp-rest-post-types-controller.php

Trac ticket: https://core.trac.wordpress.org/ticket/65817

Use of AI Tools

AI assistance: Yes
Tool(s): Google Antigravity
Model(s): Gemini 3.8 Flash
Used for: Assisting with static analysis archaeology, tests, and diff preparation; all code and tests were manually reviewed, verified, and locally run by me.

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