Work around Electron Windows command-line args quirk (#53510)

Summary:
Pull Request resolved: #53510

Changelog: [Internal]

Electron imposes a [strange undocumented limitation](electron/electron#13039) on the format of command-line arguments, which for some reason only affects Windows. Basically, the command line is truncated after the first argument that looks like a URL.

Electron's recommendation for avoiding this is to prefix the argument list with `--`,  but I prefer switching to a different arg format (`--x=y` instead of `--x y`) that will prevent us from ever running into this issue.

NOTE: I will follow up with a diff to harden arg parsing in our Electron code so that it only accepts the `--x=y` format.

Reviewed By: huntie

Differential Revision: D81237713

fbshipit-source-id: a255dc63b6486b96d9f7ccf780d1b09bc4ddf7e0

Author: motiz88

packages/dev-middleware/src/utils/DefaultBrowserLauncher.js

@@ -74,7 +74,7 @@ const DefaultBrowserLauncher = {
     windowKey: string,
   ): Promise<void> {
     return await unstable_spawnDebuggerShellWithArgs(
-      ['--frontendUrl', url, '--windowKey', windowKey],
+      ['--frontendUrl=' + url, '--windowKey=' + windowKey],
       {
         mode: 'detached',
         flavor: process.env.RNDT_DEV === '1' ? 'dev' : 'prebuilt',