Slim down WorkspaceManager

Problem/Motivation

In #3550942: Add the ability to move content between workspaces we need to use workspaces.manager in workspace.association, but we can't because at the moment we have the reverse dependency in place (the workspace manager requires the workspace association service).

Additionally, #3486378: [Plan] Allow for / implement simplified content workflow with workspaces will enable the Workspaces module on a lot more sites, and, even if it's just working under the hood, we need to ensure that it's as fast and least disruptive as possible.

Proposed resolution

Deprecate WorkspaceManagerInterface::purgeDeletedWorkspacesBatch() and move the revision purging code to WorkspacesHooks::cron() - this allows to remove the WorkspaceAssociation and State dependencies

Add WorkspaceSwitchEvent and move clearing various static caches to an event subscriber - this allows us to remove the EntityMemoryCache and WorkspaceInformation dependencies; we do need to add event_dispatcher as a new dependency, but we use a service closure to ensure that it's only instantiated when needed

Remove the logging when a workspace could not be activated (the access exception is kept) - this log message is useless and it allows us to remove the AccountProxyInterface and LoggerInterface dependencies

Remaining tasks

Review.

User interface changes

Nope.

Introduced terminology

N/A

API changes

- a deprecation: \Drupal\workspaces\WorkspaceManagerInterface::purgeDeletedWorkspacesBatch()
- an API addition: \Drupal\workspaces\Event\WorkspaceSwitchEvent

Data model changes

Nope.

Release notes snippet

TBD.