Other in Graphics
Add hasContent() to decouple this concept from having a pixmap.
Text selections historically always had pixmaps so were considered to always have content. With this new method, we will slowly be able to migrate away from this and support creating text selections that are only borders (contain no text and will not mutate document-is-modified state) i.e. you will be able to drag out text boxes and cancel them without affecting the document-is-modified flag.