Allow view access of template rest endpoint to anyone with the edit_post capability

[fabiankaegy]

What?

Part of #60316 as requested in #58301 (comment)

Modify the template / template part rest endpoint to allow any user role with the edit_post capability to view entities.

Why?

In order to render the block template in the locked template preview inside the post editor we need to be able to fetch the contents of any block templates / template parts for any user role that can edit a post.

How?

Overwriting the get_items_permissions_check and get_item_permissions_check methods of the rest_controller_class of the wp_template post type to check whether the current user can edit_posts.

Testing Instructions

Try making an authenticated rest request to the template rest endpoint with any user role that has the edit_post capability. -> The template should get returned
Try making an unauthenticated request and still get an unauthorized error

[github-actions]

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Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>
Co-authored-by: TimothyBJacobs <timothyblynjacobs@git.wordpress.org>

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[TimothyBJacobs]

You need to make a more thorough check here, right now this won't account for users who have the ability not to edit posts, but other CPTs that use the block editor. See WP_REST_Block_Types_Controller::check_read_permission for an example.

[fabiankaegy]

@TimothyBJacobs Thanks for much for your review :) I've updated the code to essentially match the example you've provided.