Screen curtain check for success

[seanbudd]

Is your feature request related to a problem? Please describe.

The screen curtain relies on an unreliable API for WOW64 applications like NVDA. If it fails silently on an untested version of Windows, personal or confidential information may be exposed on the display without a user knowing.

Describe the solution you'd like

Add a check for success when using the screen curtain.

Ensure it:

• captures all displays
• relies on a low level, reliable windows API, eg winGDI
• can be confident in the success of the screen capture (eg an empty buffer after a failed copy could look result in a black, empty bitmap)
• can be confident in the analysis of the screen capture
• is fast, as iterating over many pixels is slow in python.

Describe alternatives you've considered

There are multiple options for implementing the check, using an API like winGDI

• Using the wxWidgets API
  • a simple and fast, but not complete API. We would need to ensure the API is reliable as well.
• Using the NVDA screenBitmap module
  • slow as it requires iterating over pixels within Python to check the image
• A custom NVDA C++ implementation
  • requires dev time but can ensure no unintended changes compared to using an intermediate API

Additional context

See #12491

[feerrenrut]

We won't let this block the release, but we do want to keep making progress on this.