App Passwords: Improve validation and sanitization of the application name.

Application names are now required to be unique and cannot contain solely whitespace characters. Additionally, invalid characters are now stripped from the application name using `sanitize_text_field()`.

Props Boniu91, hellofromTonya, engahmeds3ed, xkon, francina.
Fixes #51941.


git-svn-id: https://develop.svn.wordpress.org/trunk@50030 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-application-passwords-controller.php

@@ -631,6 +631,8 @@ class WP_REST_Application_Passwords_Controller extends WP_REST_Controller {
 					'type'        => 'string',
 					'required'    => true,
 					'context'     => array( 'view', 'edit', 'embed' ),
+					'minLength'   => 1,
+					'pattern'     => '.*\S.*',
 				),
 				'password'  => array(
 					'description' => __( 'The generated password. Only available after adding an application.' ),