### 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
ElectronBrowserClient::CreateSpeechRecognitionManagerDelegate() {
  return new ElectronSpeechRecognitionManagerDelegate;
}
content::TtsPlatform* ElectronBrowserClient::GetTtsPlatform() {
  return nullptr;
}
void ElectronBrowserClient::OverrideWebkitPrefs(
    content::WebContents* web_contents,
    blink::web_pref::WebPreferences* prefs) {
  prefs->javascript_enabled = true;
  prefs->web_security_enabled = true;
  prefs->plugins_enabled = true;
  prefs->dom_paste_enabled = true;
  prefs->allow_scripts_to_close_windows = true;
  prefs->javascript_can_access_clipboard = true;
  prefs->local_storage_enabled = true;
  prefs->databases_enabled = true;
  prefs->application_cache_enabled = true;
  prefs->allow_universal_access_from_file_urls = true;
  prefs->allow_file_access_from_file_urls = true;
  prefs->webgl1_enabled = true;
  prefs->webgl2_enabled = true;
  prefs->allow_running_insecure_content = false;
  prefs->default_minimum_page_scale_factor = 1.f;
  prefs->default_maximum_page_scale_factor = 1.f;
  prefs->navigate_on_drag_drop = false;
#if !BUILDFLAG(ENABLE_PICTURE_IN_PICTURE)
  prefs->picture_in_picture_enabled = false;