Change priority of `wp_resource_hints()` to print them earlier

[ocean90]

As noted in ​https://wordpress.org/support/topic/ordering-of-dns-prefetch-preconnect?replies=2, the resource hints should be printed before scripts and styles are returned.

The current priority is 10 for wp_head and for the admin we're using admin_head which runs after admin_print_scripts. We can lower the priority to 1 for the front end and should change the admin hook to admin_print_styles.

[ocean90]

Discovered a few more things:

• Resource hints are missing in the Customizer.
• Resource hints are missing on wp-login.php.
• The filter in wp-admin/includes/admin-filters.php should be in wp-includes/default-filters.php, this will fix the Customizer.

[swissspidy]

What do you think of 37317.2.diff​?

[peterwilsoncc]

In 37317.2.diff​ customizer outputs the hints twice, above DOCTYPE declaration.

Additional thoughts

• On wp_head setting the priority to 2 seems a surer way of ensuring it follows the enqueue action.
• Using 1000 as a magic number for admin_enqueue_scripts doesn't thrill me, a low number on admin_print_scripts seems more likely to get the desired result.

[ocean90]

Replying to peterwilsoncc:

• Using 1000 as a magic number for admin_enqueue_scripts doesn't thrill me, a low number on admin_print_scripts seems more likely to get the desired result.

Did you mean admin_print_styles here? Because admin_print_scripts runs after styles are printed.

[peterwilsoncc]

Replying to ocean90:

Did you mean admin_print_styles here? Because admin_print_scripts runs after styles are printed.

I did, yes.

[ocean90]

37317.3.diff​ uses customize_controls_print_styles and admin_print_styles with a ! is_customize_preview() condition to prevent adding hints twice to the customizer.

[peterwilsoncc]

Looks good to me.

[ocean90]

In 38046:

Resource Hints: Increase priority of wp_resource_hints() so hints get printed before scripts and styles.

Also run wp_resource_hints() on the login screen and in the customizer.

Props swissspidy.
Fixes #37317.