[file_selector] Migrate file_dialog_controller to Dart.

[eugerossetto]

We're setting the basis for the 1-on-1 migration from c++ to Dart. This PR is intended to collect feedback and validate our approach.

Things we have done:

• Migrate the file_dialog_controller.cpp class to Dart using the win32 package.
• Add tests and fake classes where needed.

Things that need validation:

• Changed some of the signatures:
  • Due to constraints of the ffi Pointers, we used COMObject pointers.
  • Instead of returning an HRESULT, this implementation returns int, cloning the signature of the methods exposed by the API.
• The GetResults method uses queryInterface, to migrate it to Dart this uses the Win32 package that offers a wrapper over it that allows us to retrieve a pointer to a different supported interface.
• There is no built-in clone method in Dart. In addition to this, as the default constructor has been rewritten, there is no way of passing a FileDialogController as an input parameter.

Issue: #112212 [file_selector_windows] Migrate CPP implementation to Dart.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.