Convert shortcut_link_edit to a Controller

I created a seperate Elements file, so it can be used in both link add and link edit.
Furthermore I made the changes to make everything work by controller.

+++ b/core/modules/shortcut/lib/Drupal/shortcut/Access/LinkEditAccessCheck.php
@@ -0,0 +1,38 @@
+}

There should be an enter at the end (multiple).

+++ b/core/modules/shortcut/lib/Drupal/shortcut/Form/Elements.php
@@ -0,0 +1,69 @@
+  /**
+   * Constructs a BookManager object.

Should be {@inheritdoc} right?

Made changes according to #4.

Just re-rolled the previous patch with the changes suggested. However, I see that the menu style for admin/config/user-interface/shortcut/link still needs to be changed to new routing system.
Should the status be changed to "needs work"? Or will that part be taken care of in some other issue?

No, that should be fixed in this issue. This definitely needs work! ;)

As long as the routing.yml and the hook_menu aren't changed, none of the code of the patch is tested. So that needs to be in this patch.

I updated routing.yml and hook_menu(). The access check was identical to the one used for shortcut_link_delete, so rolled them into one.

#8: 1978972-8-shortcut-controller_conversion.patch queued for re-testing.

This needs to add/change the same code as #1978966: Convert shortcut_link_add and shortcut_link_edit to a Controller, merging them.