Tests: Bring some modernization to `wp_insert_post()` tests.

Includes:
* Using `assertIsInt()` instead of `assertIsNumeric()` for post IDs.
* Using consistent variable names for post data and retrieved posts.
* Removing added filters before performing assertions, not after.
* Removing unused `Tests_Post::$post_ids` property.
* Correcting the order of arguments in some assertions.
* Converting some `foreach()` loops to data providers.
* Wrapping long lines for better readability.

Follow-up to [13/tests], [14/tests], [167/tests], [496/tests], [1174/tests], [1246/tests], [1287/tests], [1307/tests], [1326/tests], [30510], [33261], [33630], [34762], [46279], [50012], [51438].

See #55652.
Built from https://develop.svn.wordpress.org/trunk@53782


git-svn-id: http://core.svn.wordpress.org/trunk@53341 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53781';
+$wp_version = '6.1-alpha-53782';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.