Replace get_blog_details() usage in wp-admin/my-sites.php with get_site()

[flixos90]

See #37102

[iamfriendly]

Replaced get_blog_details() with get_site() in wp-admin/my-sites.php

[iamfriendly]

In 38348.diff Replaced get_blog_details() with get_site() in wp-admin/my-sites.php

[jeremyfelt]

$site_id is added as a global in ms-settings.php (unfortunately), so I'm a little wary of reassigning it here just for the purpose of calling get_site() just in case someone is relying it.

Let's stick to the existing format and pass (int) $_POST['primary_blog']; directly to get_site().

[jeremyfelt]

In 38823:

Multisite: Replace get_blog_details() in wp-admin/my-sites.php with get_site().

Props spacedmonkey, iamfriendly.
See #37102.
Fixes #38348.