[TASK] Initial TYPO3 v14 compatibility

[garvinhicking]

This patch includes initial patches to allow requiring this package in TYPO3 v14.0-dev:

• Raise composer version compatibility
• Raise major BP version
• Drop v12 support
• Alter README to indicate v13/v14 support, removed v12 support
• BC: Use TYPO3\CMS\Core\Resource\FileType::... instead of old TYPO3\CMS\Core\Resource\File::...
• BC: Use ViewFactoryInterface to replace StandaloneViews

Note: "composer install" and CI of this patch does NOT yet work, also due to cross-dependencies like EXT:container that doesn't allow installing 14.0.x-dev yet.

Will try to maintain this as I go along with v14 development in my fork and face issues.

[garvinhicking]

(Please note, I have not adapted CI checks/testing)

[garvinhicking]

Added ViewHelper migration to use ViewFactory after v14-breaking change.

Note a 'composer install' currently doesn't work due to EXT:container cross-dependency not working in v14 yet. Current state in a v14 instance seems to work superficially.

[benjaminkott]

Changes are picked now, will close this pr - thx @garvinhicking