### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

main

### What operating system are you using?

All OSes.

### What arch are you using?

All archs.

### Last Known Working Electron version

N/A

### Expected Behavior

[`ElectronBrowserClient::GetDefaultDownloadDirectory()`](https://github.com/electron/electron/blob/main/shell/browser/electron_browser_client.cc#L1013-L1019) is hardcoded to return `~/Downloads`. However, this might not be the actual downloads directory path (eg: if the user has changed it or on OSes which translate user directory names).

The proper way to get the current user's downloads directory is OS-dependent:
- On Linux it is set in the env var `$XDG_DOWNLOAD_DIR` 
- On Windows it is returned by [`SHGetKnownFolderPath`](https://docs.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shgetknownfolderpath) passing in `FOLDERID_Downloads`
- On MacOS it is returned by [`URLForDirectory`](https://developer.apple.com/documentation/foundation/nsfilemanager/1407693-urlfordirectory) passing in `NSDownloadsDirectory`

### Current Behavior

`~/Downloads` is [hardcoded](https://github.com/electron/electron/blob/main/shell/browser/electron_browser_client.cc#L1013-L1019).

shell/browser/electron_browser_client.cc
const std::string& process_type) {
  base::FilePath dumps_path;
  base::PathService::Get(electron::DIR_CRASH_DUMPS, &dumps_path);
  {
    ANNOTATE_SCOPED_MEMORY_LEAK;
    bool upload = ElectronCrashReporterClient::Get()->GetCollectStatsConsent();
    breakpad::CrashHandlerHostLinux* crash_handler =
        new breakpad::CrashHandlerHostLinux(process_type, dumps_path, upload);
    crash_handler->StartUploaderThread();
    return crash_handler;
  }
}
int GetCrashSignalFD(const base::CommandLine& command_line) {
  
  if (command_line.HasSwitch(extensions::switches::kExtensionProcess)) {
    static breakpad::CrashHandlerHostLinux* crash_handler = nullptr;
    if (!crash_handler)
      crash_handler = CreateCrashHandlerHost("extension");
    return crash_handler->GetDeathSignalSocket();
  }
  std::string process_type =
      command_line.GetSwitchValueASCII(::switches::kProcessType);
  if (process_type == ::switches::kRendererProcess) {
    static breakpad::CrashHandlerHostLinux* crash_handler = nullptr;