Replace $wpdb->blogid with get_current_blog_id()

[spacedmonkey]

Similar to #41507 currently the class level property of blogid is reference through the code. These should be replaced with get_current_blog_id() function calls.

[bnap00]

final patch

[spacedmonkey]

Thanks for the patches @bnap00 . Some quick notes.

• In the switch_to_blog / restore tests, put the $wpdb->blogid. The test is testing that value has changed. That is one example that we can't remove it, as it invalidates the test.
• Check all functions, if that function no longer needs the global $wpdb and update the documentation. See wpmu_update_blogs_date and ms_upload_constants as example.
• Restore wp_get_db_schema back to $wpdb->blogid. This seems to be a special case where get_current_blog_id will not work as it is loaded early.

[jeremyfelt]

Thanks for your work on this, @bnap00.

In cases where value is used more than once in a function, and where extra clarity is not needed, I think it's safe to store locally for reuse ($site_id = get_current_blog_id()) instead of calling the function multiple times. The best (maybe the only) example is probably src/wp-admin/includes/upgrade.php.

And, less important, return $blogs[get_current_blog_id()]; can be updated to return $blogs[ get_current_blog_id() ]; for coding standards.

[spacedmonkey]

In 41684.2.patch I fixed the last of the formatted issues raised by @jeremyfelt .

[jeremyfelt]

In 41684.3.diff​:

• Fix the order of the arguments passed to $wpdb-prepare() in the 3rd query.
• In upgrade_280(), call refresh_blog_details() without an argument, which will refresh the current blog anyway.
• Move $site_id = get_current_blog_id() into conditional blocks where appropriate.

[jeremyfelt]

In 41661:

Multisite: Use get_current_blog_id() instead of $wpdb->blogid.

get_current_blog_id() is more appropriate for determining the ID of the current site in most cases. This eliminates the need for the global $wpdb in several functions and is better than the implicit global used in admin pages.

Props bnap00, spacedmonkey.
Fixes #41684.

[ocean90]

Follow-up: #42641