Add SERIAL_FLOAT_PRECISION option (#18367)

Marlin/src/core/serial.h

@@ -286,6 +286,12 @@ extern uint8_t marlin_debug_flags;
 
 #define SERIAL_ECHO_TERNARY(TF, PRE, ON, OFF, POST) serial_ternary(TF, PSTR(PRE), PSTR(ON), PSTR(OFF), PSTR(POST))
 
+#if SERIAL_FLOAT_PRECISION
+  #define SERIAL_DECIMAL(V) SERIAL_PRINT(V, SERIAL_FLOAT_PRECISION)
+#else
+  #define SERIAL_DECIMAL(V) SERIAL_ECHO(V)
+#endif
+
 //
 // Functions for serial printing from PROGMEM. (Saves loads of SRAM.)
 //