Restore Metro log streaming via CLI flag (#49356)

Summary:
This change adds an opt-in to restore JavaScript log streaming via the Metro dev server, [removed from React Native core in 0.77](https://reactnative.dev/blog/2025/01/21/version-0.77#removal-of-consolelog-streaming-in-metro).

Users can opt into this legacy behaviour by adding the `--client-logs` flag to `npx react-native-community/cli start`.

- The default experience remains without streamed JS logs.
- The existing "JavaScript logs have moved! ..." notice is printed in all cases, and we do not advertise the new flag for new users.
- Under non-Community CLI dev servers (i.e. Expo), log streaming is restored implicitly.

We will clean up this functionality again when we eventually remove JS log streaming over `HMRClient`, tasked in T214991636.

**Implementation notes**

- Logs are always sent over `HMRClient` (previous status quo), even with log streaming off in the dev server. This is a necessary evil to be able to flag this functionality in a user-accessible place, and to move fast for 0.78.
- Necessarily, emitting `fusebox_console_notice` moves to the dev server itself, on first device (Fusebox) connection.

Changelog:
[General][Added] - Add opt in for legacy Metro log streaming via `--client-logs` flag

packages/community-cli-plugin/src/commands/start/index.js

@@ -95,6 +95,14 @@ const startCommand: Command = {
       name: '--no-interactive',
       description: 'Disables interactive mode',
     },
+    {
+      name: '--client-logs',
+      description:
+        '[Deprecated] Enable plain text JavaScript log streaming for all ' +
+        'connected apps. This feature is deprecated and will be removed in ' +
+        'future.',
+      default: false,
+    },
   ],
 };
 

packages/community-cli-plugin/src/commands/start/runServer.js

@@ -44,6 +44,7 @@ export type StartCommandArgs = {
   config?: string,
   projectRoot?: string,
   interactive: boolean,
+  clientLogs: boolean,
 };
 
 async function runServer(
@@ -96,6 +97,11 @@ async function runServer(
       require.resolve(plugin),
     );
   }
+  // TODO(T214991636): Remove legacy Metro log forwarding
+  if (!args.clientLogs) {
+    // $FlowIgnore[cannot-write] Assigning to readonly property
+    metroConfig.server.forwardClientLogs = false;
+  }
 
   let reportEvent: (event: TerminalReportableEvent) => void;
   const terminal = new Terminal(process.stdout);