Fix local form data when form isn't mounted

If the form isn't on the page (e.g. if we're read-only), then
useFormData will return no values. In these cases, we can simply fall
back to the initialState values, as they'll either be: the default
values on a new form, or: the current values on an active create/edit
form.

Updates the manual type of useFormData to reflect this "maybe" fact.

x-pack/plugins/security_solution/public/detections/components/rules/step_define_rule/index.tsx

@@ -117,10 +117,12 @@ const StepDefineRuleComponent: FC<StepDefineRuleProps> = ({
  schema,
  });
  const { getFields, reset, submit } = form;
- const [{ index, ruleType }] = (useFormData<DefineStepRule>({
+ const [{ index: formIndex, ruleType: formRuleType }] = (useFormData({
  form,
  watch: ['index', 'ruleType'],
- }) as unknown) as [DefineStepRule];
+ }) as unknown) as [Partial<DefineStepRule>];
+ const index = formIndex || initialState.index;
+ const ruleType = formRuleType || initialState.ruleType;
  const [
  { browserFields, indexPatterns: indexPatternQueryBar, isLoading: indexPatternLoadingQueryBar },
  ] = useFetchIndexPatterns(index, RuleStep.defineRule);

x-pack/plugins/security_solution/public/detections/components/rules/step_rule_actions/index.tsx

@@ -92,10 +92,11 @@ const StepRuleActionsComponent: FC<StepRuleActionsProps> = ({
  schema,
  });
  const { getFields, submit } = form;
- const [{ throttle }] = (useFormData<ActionsStepRule>({
+ const [{ throttle: formThrottle }] = (useFormData({
  form,
  watch: ['throttle'],
- }) as unknown) as [ActionsStepRule];
+ }) as unknown) as [Partial<ActionsStepRule>];
+ const throttle = formThrottle || initialState.throttle;
 
  const handleSubmit = useCallback(
  (enabled: boolean) => {