iOS App has no attribute 'hide_cursor'

[massenz]

Describe the bug
Calling the method hide_cursor() on a toga.App causes the app to crash with:

2021-03-28 13:35:22.700314-0700 Find [938:323815] AttributeError: 'App' object has no attribute 'hide_cursor'

To Reproduce
Steps to reproduce the behavior:

1. Create a simple iOS App
2. inside the main method of your application class (derived from toga.App) call: self.hide_cursor()
3. App crashes with stacktrace
4. See error

 Error in long running handler: 'App' object has no attribute 'hide_cursor'
 Traceback (most recent call last):
   File "/private/var/containers/Bundle/Application/75DCDE12-8E7D-4D0A-97D1-B999813DBD9B/Find.app/Library/Application Support/app_packages/toga/handlers.py", line 13, in long_running_task
     delay = next(generator)
   File "/private/var/containers/Bundle/Application/75DCDE12-8E7D-4D0A-97D1-B999813DBD9B/Find.app/Library/Application Support/app/find/app.py", line 84, in select_distance_task
     self.hide_cursor()
   File "/private/var/containers/Bundle/Application/75DCDE12-8E7D-4D0A-97D1-B999813DBD9B/Find.app/Library/Application Support/app_packages/toga/app.py", line 412, in hide_cursor
     self._impl.hide_cursor()
 AttributeError: 'App' object has no attribute 'hide_cursor'

Expected behavior
The method is documented here

Not sure what to expect, really, (the description, rather tautologically, says "hides cursors") but at the very least not to crash?

What I was really trying to achieve was to hide the keyboard from view (also because the focus() method on non-input fields seems to be a no-op?).

Screenshots
If applicable, add screenshots to help explain your problem.

Environment:

• Operating System: iOS 14.4
• Python version: 3.8
• Software versions:
  toga==0.2.15
  toga-cocoa==0.2.15
  toga-core==0.2.15

Additional context

It would be good to have a way to make the "soft" keyboard disappear in iOS, as it obscures half the screen, and Toga does not appear to have a means to achieve that.

[massenz]

Also, just noticed:

[iOS] Not implemented: Widget.focus()

which pretty much explains why this is not working.

At the moment, I'm really stuck, I'd be curious to know if anyone has ever used Toga for a real-life iOS app?