Fix: NuGet static assets

[seangwright]

Motivation

Fixes #23 by removing incorrect <Folder> items in the .csproj Also adds VS Code tasks for building the Frontend JS

Checklist

• [X] Code follows coding conventions held in this repo
• [ ] Automated tests have been added
• [ ] Tests are passing
• [ ] Docs have been updated (if applicable)
• [ ] Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

How to test

1. Update the Directory.Build.props VersionPrefix to 3.0.1
2. Set the version of Kentico.Xperience.TagManager in Directory.Packages.props to 3.0.1
3. Uncomment the LocalPackages package pattern for Kentico.Xperience.TagManager in the nuget.config
4. Run the .NET pack VS Code task to create a local NuGet package
5. Run the .NET Launch (DancingGoat) - LOCAL_NUGET launch configuration to load the library from the local NuGet package
6. See the ktc-tagmanager.js script loads correctly

Note: These steps are also outlined in the docs.