Offer to "git clone" the Flutter repo to a location of users choice if no SDK is found (and "git" is available) #4532
Description
Splitting from #226 since Dart/Flutter would be different paths.
Currently if we don't find a Flutter SDK, we show a prompt to the user with a "Locate SDK" button that lets them browse (using a file picker) to where they have downloaded it. We validate this is an SDK and write it into the dart.flutterSdkPath setting.
We could consider adding an additional button to this prompt "Download SDK" that will ask the user (via a file picker) where they'd like to download it, and we can just "git clone" it for them, set the dart.flutterSdkPath setting, and run the Flutter: Run Flutter Doctor command at the end.
If we can't find git we could link them to a page on the website telling them to get git first.