add 57600 as baud selection

(cherry picked from commit d9b3f2f)

libs/core/_locales/core-strings.json

@@ -8,6 +8,7 @@
   "AcceleratorRange.TwoG": "The accelerator measures forces up to 2 gravity",
   "AcceleratorRange.TwoG|block": "2g",
   "BaudRate.BaudRate115200|block": "115200",
+  "BaudRate.BaudRate56700|block": "57600",
   "BaudRate.BaudRate9600|block": "9600",
   "BeatFraction.Eighth|block": "1/8",
   "BeatFraction.Half|block": "1/2",

libs/core/enums.d.ts

@@ -339,6 +339,8 @@ declare namespace motors {
     declare enum BaudRate {
     //% block=115200
     BaudRate115200 = 115200,
+    //% block=57600
+    BaudRate56700 = 57600,
     //% block=9600
     BaudRate9600 = 9600,
     }

libs/core/serial.cpp

@@ -12,6 +12,8 @@ enum SerialPin {
 enum BaudRate {
   //% block=115200
   BaudRate115200 = 115200,
+  //% block=57600
+  BaudRate56700 = 57600,
   //% block=9600
   BaudRate9600 = 9600
 };