Add user-toggleable setting to turn off display between refreshes,
which helps mitigate the sunlight fading issue on e-ink displays.
Changes:
- Add turnOffScreen parameter to HalDisplay methods
- Add fadingFix member and setFadingFix() to GfxRenderer
- Add fadingFix setting to CrossPointSettings with persistence
- Add "Sunlight Fading Fix" toggle in Display settings
- Update SDK submodule with turnOffScreen support
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