renderdiff: add viewer for image differences (#8768)

- Modify the compare script to output more details of a
   comparison. This will include the source/golden directory,
   the comparison directory (the new renderings), and a file
   path to difference images if the golden does not match
   the rendered image.
 - The image_diff script can now output a TIFF that is the
   difference of two input TIFFs.
 - Add a viewer for examining the differences between rendered
   output and golden images.
 - The viewer consists of a simple server of web API endpoints
   for querying difference results (along with rendered images
   in TIFF).
 - And a web-based (html + lit-element) UI for looking at the
   rendered images and differences.

test/renderdiff/src/viewer_html/index.html

@@ -0,0 +1,36 @@
+<!--
+ Copyright (C) 2025 The Android Open Source Project
+
+ 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.
+-->
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>Diff Viewer</title>
+  <script type="module" src="./app.js"></script>
+  <script src="https://cdn.jsdelivr.net/npm/utif@3.1.0/UTIF.min.js"></script>
+  <link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400,600,700" rel="stylesheet">
+  <style>
+    html, body {
+      height: 100%;
+      margin: 0;
+      font-family: "Open Sans";
+    }
+  </style>
+</head>
+<body>
+  <diff-app></diff-app>
+</body>
+</html>