XWIKI-9516: Create a new Wiki API that replaces xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Implement the UI.
* Implement the old workspaces features.
XWIKI-9516: Create a new Wiki API that replaces xwiki-platform-wiki-manager and xwiki-platform-workspace.

* Implement the UI.
* Implement the old workspaces features.