Feature summary (what you would like to be able to do and where):
Sometimes I like to see effect of a change I have in mind for a high visibility protected template and Lua in English Wikipedia if the change I'm going to request happens is applied but I don't have the right there so 'Show preview' button and 'Preview page with this template' options can't be used by me so the idea is to allow 'Show preview' button work even if the editor doesn't have the right to actually edit the page.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Template editors who don't have the right to edit a specific page to experiment with more ease to see effect of the change they are going to request on other pages. Sometimes templates are on that nested layers that can't be easily swapped with a /sandbox alternative.

Benefits (why should this be implemented?):
The ease of experience for editor without the right to experiment the changes.

Also purposed as a community wishlist
https://meta.wikimedia.org/wiki/Community_Wishlist/Wishes/Make_Show_Preview_button_work_in_protected_pages