Add maskShape parameter

[bma73]

Add an option to decouple the cropping and the UI masking shape, e.g. visually a circle mask is shown, but for cropping a square path is used.

maskShape

[ikbendewilliam]

Hi thank you for your PR, it seems we still need to update to github actions (our checks are broken otherwise). I can see that the formatting is wrong, please execute dart format . to format your files. The PR itself looks good so if we update the GitHub actions on our end and you can fix the formatting, it should be good to go.