Windows template update project

[stuartmorgan]

Description

Updates the Windows app template to use the new DartProject API, significantly simplifying the template.

Increments the template version, even though this isn't itself a breaking change, so that users will be prompted to update their projects rather than be broken later when the old API is removed.

Related Issues

None

Tests

I added the following tests: None; no functionality is changing.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them? Please read [Handling breaking changes].

• No, no existing tests failed, so this is not a breaking change.
• Yes, this is a breaking change.