Coding Standards: Rename $post_ID variable to $post_id in various files.

The `$post_ID` variable is [https://github.com/WordPress/WordPress-Coding-Standards/blob/546f59c67854589bb8f6b49a30e642e75ff419ad/WordPress/Sniffs/NamingConventions/ValidVariableNameSniff.php#L54 technically allowed in WPCS], as there is a global of the same name that needs to remain for backward compatibility. However, this name is mostly a remnant of legacy code, and switching to `$post_id` where appropriate brings more consistency with the rest of core.

Additionally, this commit resolves a few WPCS warnings in core:
{{{
Variable "$post_IDs" is not in valid snake_case format
}}}

This affects:
* Function parameters in:
 * `add_meta()`
 * `post_preview()`
 * `WP_Embed::delete_oembed_caches()`
 * `WP_Embed::cache_oembed()`
 * `wp_get_post_cats()`
 * `wp_set_post_cats()`
 * `wp_unique_post_slug()`
 * `wp_set_post_categories()`
 * `wp_check_post_hierarchy_for_loops()`
 * `wp_add_trashed_suffix_to_post_name_for_trashed_posts()`
 * `wp_filter_wp_template_unique_post_slug()`
 * `wp_xmlrpc_server::add_enclosure_if_new()`
 * `wp_xmlrpc_server::attach_uploads()`
 * `wp_xmlrpc_server::mt_getTrackbackPings()`
* Internal variables in:
 * `wp_ajax_inline_save()`
 * `wp_ajax_set_post_thumbnail()`
 * `wp_ajax_get_post_thumbnail_html()`
 * `edit_post()`
 * `bulk_edit_posts()`
 * `wp_write_post()`
 * `WP_Embed::shortcode()`
 * `wp_insert_post()`
 * `wp_xmlrpc_server::_insert_post()`
 * `wp_xmlrpc_server::blogger_getPost()`
 * `wp_xmlrpc_server::blogger_newPost()`
 * `wp_xmlrpc_server::blogger_editPost()`
 * `wp_xmlrpc_server::blogger_deletePost()`
 * `wp_xmlrpc_server::mw_getPost()`
 * `wp_xmlrpc_server::mw_newPost()`
 * `wp_xmlrpc_server::mw_editPost()`
 * `wp_xmlrpc_server::mt_getPostCategories()`
 * `wp_xmlrpc_server::mt_setPostCategories()`
 * `wp_xmlrpc_server::mt_publishPost()`
 * `wp_xmlrpc_server::pingback_ping()`
* Hook parameters in:
 * `oembed_ttl`
 * `embed_oembed_html`
 * `wp_insert_post_parent`
 * `add_trashed_suffix_to_trashed_posts`
 * `pre_post_update`
 * `edit_attachment`
 * `attachment_updated`
 * `add_attachment`
 * `edit_post_{$post->post_type}`
 * `edit_post`
 * `post_updated`
 * `save_post_{$post->post_type}`
 * `save_post`
 * `wp_insert_post`
 * `pre_wp_unique_post_slug`
 * `wp_unique_post_slug`
 * `xmlrpc_call_success_blogger_newPost`
 * `xmlrpc_call_success_blogger_editPost`
 * `xmlrpc_call_success_blogger_deletePost`
 * `xmlrpc_call_success_mw_newPost`
 * `xmlrpc_call_success_mw_editPost`

Note: The name change only affects variable names and DocBlocks.

The change does not affect the `$post_ID` global still used in a few places.

Follow-up to [51399], [52958], [53723], [53729], [55190], [55308], [55334].

Props mahekkalola, tanjimtc71, SergeyBiryukov.
Fixes #57692.

git-svn-id: https://develop.svn.wordpress.org/trunk@55365 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme-templates.php

@@ -39,12 +39,12 @@ function wp_set_unique_slug_on_create_template_part( $post_id ) {
  *
  * @param string $override_slug The filtered value of the slug (starts as `null` from apply_filter).
  * @param string $slug          The original/un-filtered slug (post_name).
- * @param int    $post_ID       Post ID.
+ * @param int    $post_id       Post ID.
  * @param string $post_status   No uniqueness checks are made if the post is still draft or pending.
  * @param string $post_type     Post type.
  * @return string The original, desired slug.
  */
-function wp_filter_wp_template_unique_post_slug( $override_slug, $slug, $post_ID, $post_status, $post_type ) {
+function wp_filter_wp_template_unique_post_slug( $override_slug, $slug, $post_id, $post_status, $post_type ) {
 	if ( 'wp_template' !== $post_type && 'wp_template_part' !== $post_type ) {
 		return $override_slug;
 	}
@@ -61,7 +61,7 @@ function wp_filter_wp_template_unique_post_slug( $override_slug, $slug, $post_ID
 	 * to the entity. So for now we use the currently activated theme for creation.
 	 */
 	$theme = get_stylesheet();
-	$terms = get_the_terms( $post_ID, 'wp_theme' );
+	$terms = get_the_terms( $post_id, 'wp_theme' );
 	if ( $terms && ! is_wp_error( $terms ) ) {
 		$theme = $terms[0]->name;
 	}
@@ -71,7 +71,7 @@ function wp_filter_wp_template_unique_post_slug( $override_slug, $slug, $post_ID
 		'post_type'      => $post_type,
 		'posts_per_page' => 1,
 		'no_found_rows'  => true,
-		'post__not_in'   => array( $post_ID ),
+		'post__not_in'   => array( $post_id ),
 		'tax_query'      => array(
 			array(
 				'taxonomy' => 'wp_theme',