Feature: #96904 - Backend toolbar items are request aware 

See forge#96904

Description 

When registering own toolbar items to the TYPO3 backend top bar, classes can now retrieve the current PSR-7 request by implementing \TYPO3\CMS\Backend\Toolbar\RequestAwareToolbarItemInterface . This is especially useful when rendering views using \TYPO3\CMS\Backend\View\BackendViewFactory which depends on current request.

Impact 

The TYPO3 Core encourages to use BackendViewFactory instead of StandaloneView when toolbar items of extensions use Fluid templates. BackendViewFactory has a dependency to current request, so RequestAwareToolbarItemInterface should be implemented to receive the current request from TYPO3 EXT:backend.

Doing so enables the template overrides by TSconfig feature.