keyboardFor method
How tall this device's keyboard is when a field asks for variant.
The one place a variant becomes a number, so nothing downstream has to know which variants differ on which platform — an iPad answers the same height for all four, and that is a property of the iPad rather than something a caller should special-case.
Already turned: call it on the device oriented gave you.
Implementation
double keyboardFor(KeyboardVariant variant) =>
keyboardHeightFor(variant, letters: keyboard, keypad: keypadKeyboard);