Currently, there are a number of scenarios where `is_block_editor()` (and `WP_Screen::is_block_editor`) would incorrectly indicate block editor support at different points of the loading process. Most notably, checking `is_block_editor` when hooking into the `current_screen` action will always result in `false`, even when the block editor is being loaded. This is because `is_block_editor` is not set to `true` until `edit-form-blocks.php` is included.
This change adds logic to `WP_Screen` to ensure the accuracy of `is_block_editor` on block editor pages earlier in the load process.
While edit screens will now be accurate 100% of the time from `current_screen` on, there are still a few edge cases where `is_block_editor` could contain an incorrect value when creating a new post.
Because a `WP_Post` object is a required parameter for the `replace_editor` filter and `use_block_editor_for_post()` function, `WP_Screen` will fall back to the value returned by `use_block_editor_for_post_type()` for the post being created. To eliminate these edge cases, the `use_block_editor_for_post_type` filter can be used to return the appropriate boolean value to indicate support.
Props Chouby, desrosj, aduth, johnbillion.
Fixes#46195.
git-svn-id: https://develop.svn.wordpress.org/trunk@45224 602fd350-edb4-49c9-b593-d223f7449a82
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