GitLab

Add shortcut to copy file content hash link

## What does this MR do?

* Allows for multiple shortcut handlers to be initialised
* Adds `y` shortcut to file pages to copy permalink URL.

## Are there points in the code the reviewer needs to double check?

Ney.

## Why was this MR needed?

UX

## What are the relevant issue numbers?

Closes #14470.

## Screenshots (if relevant)

![y-shortcut](/uploads/b81feb26d8e0d7d4996c4afa29f385d7/y-shortcut.gif)

See merge request !4496