Webui small fixes (#3713)

esphome/core/helpers.cpp

@@ -258,6 +258,19 @@ std::string value_accuracy_to_string(float value, int8_t accuracy_decimals) {
   return std::string(tmp);
 }
 
+int8_t step_to_accuracy_decimals(float step) {
+  // use printf %g to find number of digits based on temperature step
+  char buf[32];
+  sprintf(buf, "%.5g", step);
+
+  std::string str{buf};
+  size_t dot_pos = str.find('.');
+  if (dot_pos == std::string::npos)
+    return 0;
+
+  return str.length() - dot_pos - 1;
+}
+
 // Colors
 
 float gamma_correct(float value, float gamma) {