core-api: refactor FeatureFlagApi to register flags instead of assigning

plugins/user-settings/src/components/FeatureFlags/FeatureFlags.tsx

@@ -17,7 +17,7 @@
 import React, { useCallback, useState } from 'react';
 import {
   featureFlagsApiRef,
-  FeatureFlagsRegistryItem,
+  FeatureFlag,
   FeatureFlagState,
   InfoCard,
   useApi,
@@ -30,7 +30,7 @@ export const FeatureFlags = () => {
   const featureFlagsApi = useApi(featureFlagsApiRef);
   const featureFlags = featureFlagsApi.getRegisteredFlags();
   const initialFlagState = featureFlags.reduce(
-    (result, featureFlag: FeatureFlagsRegistryItem) => {
+    (result, featureFlag: FeatureFlag) => {
       const state = featureFlagsApi.getFlags().get(featureFlag.name);
 
       result[featureFlag.name] = state;

plugins/user-settings/src/components/FeatureFlags/FeatureFlagsItem.tsx

@@ -22,10 +22,10 @@ import {
   Switch,
   Tooltip,
 } from '@material-ui/core';
-import { FeatureFlagsRegistryItem } from '@backstage/core';
+import { FeatureFlag } from '@backstage/core';
 
 type Props = {
-  flag: FeatureFlagsRegistryItem;
+  flag: FeatureFlag;
   enabled: boolean;
   toggleHandler: Function;
 };