kcms/tablet: Add a confirmation before saving calibration settings

There's still a UX issue with the calibration tool, where it's easy to create a broken calibration matrix that makes the device unusable and there's no clear way to reset it back to a usable state.

This tries to fix it from multiple angles:

1. Add a reset timer and a new confirmation stage to the calibration process. This should ensure the user has consciously tested the new calibration before stopping the process.
2. Add a reset button next to the "Calibrate" button to reset it back to default. This does the same thing as the "Defaults" button without resetting the rest of your tablet settings.
3. Add a label that states that if your tablet no longer works, try resetting the calibration matrix first.

Screenshots

BUG: 494467