Fix Devcontainer build errors (#4647)

Devcontainer Dockerfile has been updated to use Ubuntu 24.04 as the
base. Now devcontainer builds without errors. Tested with Podman on
Linux and Docker Desktop on Windows.

To avoid re-downloading and re-compiling whenever the container is
deleted, a named volume is mounted at /home/ubuntu/.cache.

Closes #4065

.devcontainer/devcontainer.json

@@ -5,8 +5,22 @@
 {
   "name": "carbon-lang",
   "build": {
-    "dockerfile": "../docker/ubuntu2204/base/Dockerfile"
+    "dockerfile": "../docker/ubuntu2404/base/Dockerfile"
   },
+  "mounts": [
+    {
+      "source": "carbon-cache",
+      "target": "/home/ubuntu/.cache",
+      "type": "volume"
+    }
+  ],
+  "containerUser": "ubuntu",
+  "remoteUser": "ubuntu",
+  // When using devcontainer with podman, you may see /workspace being owned
+  // by root. To work around this, uncomment the following lines
+  // "runArgs": [
+  //   "--userns=keep-id"
+  // ],
   "customizations": {
     "vscode": {
       "extensions": [