Remove invariant code from Configurations

- Add `Conditionals.h` with calculated configuration values
- Add `SanityCheck.h` with checks for configuration errors
- Remove equivalent code from all configurations
- Move error checks from some sources to `SanityCheck.h` also
- Fix initialization of count_direction in stepper.cpp

Marlin/stepper.cpp

@@ -89,7 +89,7 @@ static bool old_x_min_endstop = false,
 static bool check_endstops = true;
 
 volatile long count_position[NUM_AXIS] = { 0 };
-volatile signed char count_direction[NUM_AXIS] = { 1 };
+volatile signed char count_direction[NUM_AXIS] = { 1, 1, 1, 1 };
 
 
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