Provide the 32-bit Dart SDK as a fallback

This allows the extension to work out-of-the-box for users that do not have Dart installed. However, it does include a relatively large binary file. My intent was to consider linking the file externally (and including it on demand when creating the VSIX) if it needs to change frequently, or if it is provided in a reliable location e.g. within the source control repository of an official Dart project.