Security, Site Health: Improve accuracy in messaging about HTTPS support.

Following up on [49904], this changeset focuses mainly on improving the guidance about the current state of HTTPS in Site Health.

* Correct the existing copy to indicate that both the Site Address and the WordPress Address need to be changed to fully switch to HTTPS.
* Link to the respective input fields via anchor links rather than to the overall General Settings screen.
* Show different copy if the site is using HTTPS for the WordPress Address (for example to have only the administration panel in HTTPS), but not for the Site Address.
* Inform the user about potential problems even when the site is already using HTTPS, for example if the SSL certificate was no longer valid.
* Always rely on fresh information for determining HTTPS support issues in Site Health, and therefore change the `https_status` test to become asynchronous.
* Rename the new private `wp_is_owned_html_output()` function to a more appropriate `wp_is_local_html_output()`.

Props adamsilverstein, flixos90, johnjamesjacoby, timothyblynjacobs.
See #47577.


git-svn-id: https://develop.svn.wordpress.org/trunk@50072 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/rest-api/rest-schema-setup.php

@@ -137,6 +137,7 @@ class WP_Test_REST_Schema_Initialization extends WP_Test_REST_TestCase {
 			'/wp-site-health/v1',
 			'/wp-site-health/v1/tests/background-updates',
 			'/wp-site-health/v1/tests/loopback-requests',
+			'/wp-site-health/v1/tests/https-status',
 			'/wp-site-health/v1/tests/dotorg-communication',
 			'/wp-site-health/v1/tests/authorization-header',
 			'/wp-site-health/v1/directory-sizes',