Update for macOS 15 (Sequoia) and Apple Silicon

[anishathalye]

Lumen doesn't work on macOS 15 (Sequoia) / Apple Silicon. It uses old APIs that have been deprecated/removed. Among other things, this will require:

• Switching to ScreenCaptureKit for measuring the average brightness of the screen contents. This interacts with macOS's permissions model as well, so we might need to add dialog boxes to ask for permission, error messages if the user hasn't given the app permissions, etc.
• Using a new/supported API for changing screen brightness. See previous discussion in core functionality broken on my machine #26 (comment), Add experimental CoreDisplay API (fixes #26) #31, and macOS 11.5.1 m1 MBP 2020 - doesn't seem to work #35.