Per-thread service that caches page instances for the duration of the request, and is also responsible for tracking
the active page (the page which will ultimately render the response).
Since Page is internal, most user-code should use the
ComponentSource service instead.
Starting in 5.2, page instances are shared (with externalized mutable state), not pooled, but the cache is still
useful for managing the page's lifecycle.
Gets the page via its page name, in the current locale. The logical page name is resolved to a class name, which
is used to obtain the page (from the page pool). Note that under certain circumstances, a page may have multiple
names (even beyond simple case-insensitivity), and RequestPageCache caches correctly.
pageName - the name of the page to retrieve (this is the logical page name, not the fully qualified class