Split bed size sanity check into two

Marlin/src/inc/SanityCheck.h

@@ -423,8 +423,8 @@
 /**
  * Validate that the bed size fits
  */
-static_assert(X_MAX_LENGTH >= X_BED_SIZE && Y_MAX_LENGTH >= Y_BED_SIZE,
+static_assert(X_MAX_LENGTH >= X_BED_SIZE, "Movement bounds (X_MIN_POS, X_MAX_POS) are too narrow to contain X_BED_SIZE.");
-  "Movement bounds ([XY]_MIN_POS, [XY]_MAX_POS) are too narrow to contain [XY]_BED_SIZE.");
+static_assert(Y_MAX_LENGTH >= Y_BED_SIZE, "Movement bounds (Y_MIN_POS, Y_MAX_POS) are too narrow to contain Y_BED_SIZE.");
 
 /**
  * Granular software endstops (Marlin >= 1.1.7)