FEATURE: Allow to specify an image focal point in the crop-image dialog

[mficzel]

Neos might get focal point support In #5127 and to actually use this the cop-image dialog should allow to specify a focal point and visualize focal points in the inspector.

Description

• The Neos.UI should be extended and allow to specify a focal point in the crop-image dialog. The given values should then be passed as focalPointX ?int and focalPointY ?int of the new ImageVariant that is created
  via endpoint neos/content/create-image-variant which points to \Neos\Neos\Controller\Backend\ContentController::createImageVariantAction
• The Image Preview in the Inspector should visualize an existing focal point

Expected behavior

Focal points can be set and are shown in the inspector when present.

Actual behavior

... nothing so far ...

Affected Versions

Neos: 8.4

UI: 8.4