Add dropdown for boost privacy in boost confirmation modal (#15704)

* Various dropdown code quality fixes

* Prepare support for privacy selection in boost modal

* Add dropdown for boost privacy in boost confirmation modal

app/javascript/mastodon/reducers/boosts.js

@@ -0,0 +1,25 @@
+import Immutable from 'immutable';
+
+import {
+  BOOSTS_INIT_MODAL,
+  BOOSTS_CHANGE_PRIVACY,
+} from 'mastodon/actions/boosts';
+
+const initialState = Immutable.Map({
+  new: Immutable.Map({
+    privacy: 'public',
+  }),
+});
+
+export default function mutes(state = initialState, action) {
+  switch (action.type) {
+  case BOOSTS_INIT_MODAL:
+    return state.withMutations((state) => {
+      state.setIn(['new', 'privacy'], action.privacy);
+    });
+  case BOOSTS_CHANGE_PRIVACY:
+    return state.setIn(['new', 'privacy'], action.privacy);
+  default:
+    return state;
+  }
+}

app/javascript/mastodon/reducers/index.js

@@ -16,6 +16,7 @@ import push_notifications from './push_notifications';
 import status_lists from './status_lists';
 import mutes from './mutes';
 import blocks from './blocks';
+import boosts from './boosts';
 import reports from './reports';
 import contexts from './contexts';
 import compose from './compose';
@@ -57,6 +58,7 @@ const reducers = {
   push_notifications,
   mutes,
   blocks,
+  boosts,
   reports,
   contexts,
   compose,