CI check generate code (#4998)

* call reflection code generation from tests

This simplifies instructions to contributors so they don't forget to update
reflection code.

* add error handling to generate_code scripts

Let them propagate their errors instead of swallowing them so they show
up when called in CI.

* apply editorconfig to shell scripts

* use ordered map in dart codegen

Using an unordered map in the codegen can lead to spurious diffs in the
generated dart code.

* add CI check for generate_code being run

* update reflection_generated.h

* disable diff-check for monster_test.bfbs

Work around #5008.

include/flatbuffers/reflection_generated.h

@@ -94,6 +94,7 @@ inline const char * const *EnumNamesBaseType() {
 }
 
 inline const char *EnumNameBaseType(BaseType e) {
+  if (e < None || e > Union) return "";
   const size_t index = static_cast<int>(e);
   return EnumNamesBaseType()[index];
 }