Implement --version flag

Summary:
Changelog: [Internal]

Adds a basic `--version` command line flag to the RNDT shell. This will be used in code paths (including tests) that need to verify that the shell is executable, but do not need to actually display a window or hand over control to the main shell instance.

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Reviewed By: huntie

Differential Revision: D78351936

fbshipit-source-id: e8982cfea6435da0ac9ea5f50d57c7642a8e2edb

packages/debugger-shell/src/electron/index.flow.js

@@ -10,6 +10,22 @@
 
 // $FlowFixMe[unclear-type] We have no Flow types for the Electron API.
 const {app} = require('electron') as any;
+const util = require('util');
+
+// Handle global command line arguments which don't require a window
+// or the single instance lock to be held.
+const {
+  values: {version = false},
+} = util.parseArgs({
+  options: {version: {type: 'boolean'}},
+  args: process.argv.slice(app.isPackaged ? 1 : 2),
+  strict: false,
+});
+if (version) {
+  console.log(`${app.getName()} v${app.getVersion()}`);
+  // Not app.quit() - we want to exit immediately without initialising the graphical subsystem.
+  app.exit(0);
+}
 
 const gotTheLock = app.requestSingleInstanceLock({
   argv: process.argv.slice(2),