Move events constant from interface to a class

Problem/Motivation

Move events constant from \Drupal\hook_event_dispatcher\HookEventDispatcherInterface to a final class like \Symfony\Component\HttpKernel\KernelEvents

Steps to reproduce

Proposed resolution

Remaining tasks

• #3264078: Move entity hook events constant to a class
• #3264190: Move field hook events constants to a class
• #3263300: Move file hook events to a class
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::FORM_ALTER
• #3265437: Move block hook event constants to a class
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::TOKEN_REPLACEMENT
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::TOKEN_INFO
• #3265551: Move path hook event constants to a class
• #3264875: Move view hook event constants to a class
• #3265143: Move theme hook event constants to a class
• #3265541: Move user hook event constants to a class
• #3266483: Move toolbar hook event constants to a class
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::PAGE_TOP
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::PAGE_BOTTOM
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::PAGE_ATTACHMENTS
• #3265166: Move core hook event constants to a class
• \Drupal\hook_event_dispatcher\HookEventDispatcherInterface::LANGUAGE_SWITCH_LINKS_ALTER
• #3266740: Move jsonapi, media, and webform event constants to a class

User interface changes

API changes

Data model changes