feat: DTMF dialpad

dialer/android/app/src/main/kotlin/com/icing/dialer/activities/MainActivity.kt

@@ -208,6 +208,15 @@ class MainActivity : FlutterActivity() {
                         checkAndRequestDefaultDialer()
                         result.success(true)
                     }
+                    "sendDtmfTone" -> {
+                        val digit = call.argument<String>("digit")
+                        if (digit != null) {
+                            val success = MyInCallService.sendDtmfTone(digit)
+                            result.success(success)
+                        } else {
+                            result.error("INVALID_ARGUMENT", "Digit is null", null)
+                        }
+                    }
                     else -> result.notImplemented()
                 }
             }