Load Combined Core Block Assets

This is a temporary workaround for sites experiencing any issues with WordPress 6.9’s new ability to load block styles on demand in classic themes, for example #64354.

If running a classic theme (i.e. not a block theme), it filters should_load_separate_core_block_assets to be false. This has the effect of reverting a change introduced in 6.9 where classic themes now load separate core block assets on demand by default.

Note that this plugin should be considered temporary until any issues are resolved in 6.9.1. At any time, you can test whether any issues remain by adding ?should_load_separate_core_block_assets=true to any frontend URL; this restores the default behavior in WP 6.9.

This workaround is temporary because there are performance benefits to loading separate core block assets. They can be loaded on demand just when they are used, as opposed to loading the large single combined wp-block-library stylesheet. Loading separate block styles on demand reduces the amount of CSS which should improve page load time.