Feature: #93209 - FAL: Add getFile() to TYPO3CMSCoreResourceFolder

See Issue #93209

Description

The FAL Folder object now contains a new convenience method getFile().

The FolderInterface does not contain the definition yet, as this would be a breaking change, thus, a comment is added to make sure the Interface gets this addition in v12 as well.

Impact

When dealing as a developer with FAL Folder objects, the method $folder->getFile("filename.ext") can now be used instead of $folder->getStorage()->getFileInFolder("filename.ext", $folder)