Deprecation: #90348 - PageLayoutView class
See forge#90348
Description
The 
        Page class, which is considered internal API, has been marked as deprecated in favor
of the new Fluid-based alternative which renders the "page" BE module.
Impact
Implementations which depend on 
        Page should prepare to use the alternative implementation (by overlaying and overriding Fluid templates of EXT:backend).
Affected Installations
- Any site which overrides the Pageclass. The overridden class will still be instantiated when rendering previews in BE page module - but no methods will be called on the instance unless they are called by a third party hook subscriber.Layout View 
- Any site which depends on PSR-14 events associated with Pagewill only have those events dispatched if theLayout View fluidfeature flag isBased Page Module false. Affects :php:`\TYPO3\CMS\Backend\View\Event\AfterSectionMarkupGeneratedEvent`. Affects\TYPO3\.CMS\ Backend\ View\ Event\ Before Section Markup Generated Event 
Migration
Fluid templates can be extended or replaced to render custom header, footer or preview of
a given 
        CType, see feature description for feature forge#90348.