DUPP-176 Prevent rendering of the block editor script when not on an edit screen

[enricobattocchi]

Context

• We want to prevent a fatal error in the plugin's script for the Block Editor when it's executed where it's not supposed to.

A plugin or a theme may (wrongfully) set the global var $post in the Widgets screen. This, paired with the fact that the Widgets screen executes the enqueue_block_editor_assets even if there is no post to be edited, trigger the execution of out duplicate-post-edit.js script, which fails because there is no core/editor store or PluginPostStatusInfo component available.
With the FSE transition undergoing, this might happen even more frequently.

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where a fatal error would be triggered in the Widgets page in combination with some themes or plugins.

Relevant technical choices:

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

Reproduce the error

• build from master (or use any 4.* version)
• add this custom code to the end of your theme's functions.php:

function my_set_post() {
    global $post;
    $posts = get_posts();
    $post = $posts[0];
}
add_action( 'init', 'my_set_post' );

• visit Appearance > Widgets
• see that the page fails with a fatal error that can't be recovered

Test the fix

• Switch to this branch and build
• visit Appearance > Widgets
• see that the page doesn't fail anymore
• activate Yoast SEO (it's been found that it can enable certain conditions that we check)
• visit Appearance > Widgets
• see that the page doesn't fail anymore
• edit a published post with the Block editor and check that Copy to a new draft and Rewrite & Republish are visible in the Status and visibility section of the sidebar.
• create a new post with the Block editor and check that Copy to a new draft is visible in the Status and visibility section of the sidebar.

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes DUPP-176

[maartenleenders]

Acceptance 🚧 it still loads and errors:

we now tried ! ( window.wp.editPost && window.wp.editPost.PluginPostStatusInfo ) and that works better. Also you have suggested checking whether we are outside of the post editor.

[maartenleenders]

Yes that does the trick! 🎉