[Suggestion] Flip document

[kingzeroth]

*Flip View in View option does not actually flip the layers for the final image.

The current method for flipping the whole document requires selecting all the layers and folders and select the whole canvas with Ctrl+A. It quickly becomes cumbersome when there is a dozen or even few dozen of layers. A button for flipping the whole document would streamlined the whole process.

It also does not tell if the document is flipped at the moment which leads to confusion when you realize the final output image is "un-flipped" and requires you to flip everything and output the whole image again.