YAML files for menu links, contextual links, local tasks, and local actions have been renamed

YAML files for contextual links, local tasks, and local actions have been renamed to improve the developer experience. The new naming scheme makes it easier for a developer to determine what a module implements, and does not require module developers to know special names for each subsystem.

Also, the the naming is more consistent and as an added bonus makes the files appear grouped together in a directory listing.

• *.local_tasks.yml has been renamed to *.links.task.yml
• *.local_actions.yml has been renamed to *.links.action.yml
• *.contextual_links.yml has been renamed to *.links.contextual.yml
• *.menu_links.yml has been renamed to *.links.menu.yml

Also updating the prior change notices:

• Contextual Links are provided by plugins implementing ContextualLinkInterface and using YAML discovery instead of being defined in hook_menu()
• Local action links now provided by plugins using YAML discovery and implementing LocalActionInterface
• Local tasks are provided by plugins implementing LocalTaskInterface instead of type MENU_LOCAL_TASK in hook_menu()
• hook_menu_link_defaults() moved to *.links.menu.yml files