Docs: Improve documentation for wp_should_load_separate_core_block_assets().

This should clarify the purpose of the function and what effect it has on block styles loading.

Props aristath, desrosj, jorbin, SergeyBiryukov.
See #53505.

git-svn-id: https://develop.svn.wordpress.org/trunk@51256 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-loader.php

@@ -2328,6 +2328,20 @@ function wp_should_load_block_editor_scripts_and_styles() {
 /**
  * Checks whether separate assets should be loaded for core blocks on-render.
  *
+ * When this function returns true, other functions ensure that core blocks
+ * only load their styles on-render, and each block loads its own, individual
+ * stylesheet. Third-party blocks only load their styles when rendered.
+ *
+ * When this function returns false, all core block styles are loaded regardless
+ * of whether they are rendered in a page or not, because they are all part of
+ * the `block-library/style.css` file. Third-party blocks always get enqueued
+ * regardless of whether they are rendered or not.
+ *
+ * This only affects front end and not the block editor screens.
+ *
+ * @see wp_enqueue_registered_block_scripts_and_styles()
+ * @see register_block_style_handle()
+ *
  * @since 5.8.0
  *
  * @return bool Whether separate assets will be loaded.