Docs: Synchronize parameter documentation for various metadata functions, update per the documentation standards.

See #49572.

git-svn-id: https://develop.svn.wordpress.org/trunk@47611 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/meta.php

@@ -662,7 +662,7 @@ function get_metadata_by_mid( $meta_type, $meta_id ) {
  * @param string $meta_type  Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
  *                           or any other object type with an associated meta table.
  * @param int    $meta_id    ID for a specific meta row.
- * @param string $meta_value Metadata value.
+ * @param string $meta_value Metadata value. Must be serializable if non-scalar.
  * @param string $meta_key   Optional. You can provide a meta key to update it. Default false.
  * @return bool True on successful update, false on failure.
  */