Entity controller admin-form annotation replaced by field_ui_base_route

The admin-form annotation in the "links" section of Entity annotation has been replaced by field_ui_base_route (which does not go in the "links" section). This annotation gives the base route that the Field UI module should attach its Manage Fields, Manage Display, and Manage Form Display tabs to. It works the same as before; it's just annotated differently.

For example, previous to this change, the Shortcut entity would have provided this route in the "admin-form" annotation under "links":

 *   links {
 *     "admin-form" = "entity.shortcut.canonical",
...

After this change, instead put this outside of "links":

 *   field_ui_base_route = "entity.shortcut.canonical",