Tests: Refactor `Tests_Image_Functions::test_is_displayable_image_positive()` to use a data provider.

Using a data provider has a number of advantages:
1. If the first test case fails, it won't prevent the other test cases from being tested.
2. While the assertion used in this test method ''does'' have a "failure message" (👍), the output from PHPUnit itself will already be more descriptive in case of failure when using a data provider.
3. Using named test cases in the data provider will also make the `--testdox` output much more descriptive and informative.

The actual cases being tested, or the test itself have not been changed.

Includes:
* Changing the conditional addition of the `.ico` file type to be unconditional, it was only needed for PHP < 5.3.
* Adding a `@covers` annotation.

Follow-up to [184/tests], [42780], [53495], [53497], [53521], [53523], [53524].

Props jrf.
See #55652.
Built from https://develop.svn.wordpress.org/trunk@53525


git-svn-id: http://core.svn.wordpress.org/trunk@53114 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53524';
+$wp_version = '6.1-alpha-53525';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.