Fix TextInput crash on Apple M1. Add noop select_file to cocoa.app.App to prevent an exception being raised

[wtfuzz]

Added argtypes=[c_void_p] to the send_super call in TogaTextField.textDidEndEditing_()
This adds a noop mehtod for the select_file callback in toga_cocoa.app.App

TextInput crashes on Apple M1 silicon when losing focus
This exception is raised when creating a Toga app on macOS

Exception ignored on calling ctypes callback function: <rubicon.objc.api.objc_method object at 0x10796f7f0>
Traceback (most recent call last):
  File "/Users/fuzz/dev/dev-venv/lib/python3.10/site-packages/rubicon/objc/api.py", line 275, in __call__
    result = self.py_method(py_self, *args)
  File "/Users/fuzz/dev/dev-venv/lib/python3.10/site-packages/toga_cocoa/app.py", line 56, in applicationOpenUntitledFile_
    self.impl.select_file()
AttributeError: 'App' object has no attribute 'select_file'

PR Checklist:

• [ X] All new features have been tested
• [X ] All new features have been documented
• [ X] I have read the CONTRIBUTING.md file
• [ X] I will abide by the code of conduct

[freakboy3742]

Awesome! Thanks for the debugging work on this one!