Fix Site Health false OPcache warning (#65395)

[yashyadav-mo]

Fixes a false “Opcode cache is not enabled” Site Health warning on shared hosts where Zend OPcache is active but opcache_get_status() returns false because the host blocks OPcache API calls (commonly via opcache.restrict_api).

This behavior was introduced in WordPress 7.0 with the new opcode cache Site Health test (#63697).

Changes:

Add wp_opcache_is_enabled() in wp-admin/includes/file.php, alongside existing OPcache helpers. Uses opcache_get_status() when available; otherwise falls back to ini_get( 'opcache.enable' ) when the status API is unavailable.
Update WP_Site_Health::get_test_opcode_cache() to use the new helper.
Update WP_Debug_Data so restricted hosts show “Enabled (statistics unavailable due to server configuration)” instead of “Disabled by configuration”.
Add/update PHPUnit coverage in wpOpcacheIsEnabled.php and wpSiteHealth.php.
Trac ticket: https://core.trac.wordpress.org/ticket/65395

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Unlinked Accounts

The following contributors have not linked their GitHub and WordPress.org accounts: @root@MO-LT-1110.ad.xecurify.com.

Contributors, please read how to link your accounts to ensure your work is properly credited in WordPress releases.

Core Committers: Use this line as a base for the props when committing in SVN:

Props yashyadav247, yusufmudagal.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[yusufhay]

Tested the patch locally against current origin/trunk in a disposable worktree.

Results:

• php -l src/wp-admin/includes/file.php passed.
• php -l src/wp-admin/includes/class-wp-site-health.php passed.
• php -l src/wp-admin/includes/class-wp-debug-data.php passed.
• vendor/bin/phpunit --filter 'test_wp_opcache_is_enabled_returns_bool|test_wp_opcache_is_enabled_matches_environment' passed: 2 tests, 2 assertions.\n\nThe new OPcache helper coverage passes for me.