Implement interaction with printer

### What is the problem or limitation you are having?

Toga currently offers support to some hardware, like camera and computer screen, but doesn't offer direct access to printer or scanner.

### Describe the solution you'd like

The ideal implementation of this feature would be able to handle:
- Raw text
- Text files (e.g. txt or pdf)
- Image files (e.g. png or jpeg)

One pice of the content listed above would be handed to the OS-specfic print dialog, like the ones attached below, where page selection, printer selection, orientation and other configurations should happen, outside of the Toga application.

Linux (GTK):
https://docs.gtk.org/gtk4/class.PrintUnixDialog.html

Windows:

MacOS:

Android:

### Describe alternatives you've considered

Handling printers and printing in python is not very straightfoward:
- there is a package dedicated to windows `win32print`, `win32ui`
- the solution I found for Unix systems would issue a `lp` command to the system, using Python's `subprocess` package

### Additional context

_No response_

No source file or test is named. Start by clarifying the supported platforms and the API boundary using the GTK, Windows, macOS, and Android print-dialog examples, including which raw and file-based inputs are required; done means an agreed cross-platform scope and verified printer interaction.

Written by the indexing model from the issue text.