explorer: new delete alert dialog

This replaces the delete notification with a new alert dialog. This
makes for better keyboard interaction and forces the user to make a
decision before doing anything else.

Also fixes closing the editor before deleting the file.

src/explorer/deleteFileAlert/reducers.ts

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2022 The Pybricks Authors
+
+import { Reducer, combineReducers } from 'redux';
+import {
+    deleteFileAlertDidAccept,
+    deleteFileAlertDidCancel,
+    deleteFileAlertShow,
+} from './actions';
+
+/** Controls the delete file alert dialog isOpen state. */
+const isOpen: Reducer<boolean> = (state = false, action) => {
+    if (deleteFileAlertShow.matches(action)) {
+        return true;
+    }
+
+    if (
+        deleteFileAlertDidAccept.matches(action) ||
+        deleteFileAlertDidCancel.matches(action)
+    ) {
+        return false;
+    }
+
+    return state;
+};
+
+/** Controls the file name displayed in the file alert dialog. */
+const fileName: Reducer<string> = (state = '', action) => {
+    if (deleteFileAlertShow.matches(action)) {
+        return action.fileName;
+    }
+
+    return state;
+};
+
+export default combineReducers({ isOpen, fileName });