make preview useable without client list, to reuse in create link view

src/Platform.js

@@ -0,0 +1,42 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {createEnum} from "./utils/enum.js";
+
+export const Platform = createEnum(
+	"DesktopWeb",
+	"MobileWeb",
+	"Android",
+	"iOS",
+	"Windows",
+	"macOS",
+	"Linux"
+);
+
+export function guessApplicablePlatforms(userAgent) {
+	// use https://github.com/faisalman/ua-parser-js to guess, and pass as RootVM options
+	return [Platform.DesktopWeb, Platform.Linux];
+	// return [Platform.MobileWeb, Platform.Android];
+}
+
+export function isWebPlatform(p) {
+	return p === Platform.DesktopWeb || p === Platform.MobileWeb;
+}
+
+
+export function isDesktopPlatform(p) {
+	return p === Platform.Linux || p === Platform.Windows || p === Platform.macOS;
+}